In Search of the Golden Cascode (Debunking The Myth of the
Contents
1. Text Book Cascode Figure 1 Twin Triode Cascode Amplifier Courtesy of Tube Cad While a simplification in a sense the upper triode s cathode acts as a constant current source CSS for the lower triode s plate There are a few different variations but the bottom line is there will be some form of direct coupling of a cathode to a plate Additional information on cascoded pair variants such as SRPP Cascoded Cathode Follower etc can be found at http www glass ware com tubecad TC Tube Circuit Descriptions html What s a cascode front end A cascode amplifier is commonly used at radio and video frequency signal entry points aka the front end due to its high gain and low noise most specifically within the FM frequency bandwidth Immediately following the antenna entry point the front end of an FM tuner typically includes an RF amplifier local oscillator and a mixer This would be followed by a series of intermediate frequency IF amplifiers passing through the clipping windows of a sequence of amplitude limiter circuits after which the audio program is separated from its carrier within the detector prior to final amplification by the various audio frequency gain stages LIMITER DETECTOR AUDIO Figure 2 FM Tuner Sections But as most have discovered in many aspects of home audio sound you re final sonic qualities will generally only be as good as your front end and the cascode front end has ca2. Dynamic Spacexpander First stereo tuner with MicroTune First FM tuner with six IF stages First FM tuner with five limiters First front panel antenna selector switch 72 300 ohm Local Distant positions First Multiplex units with STEREO BEACON and automatic switching mono to stereo Figure 4 Fisher Firsts From a 1964 Fisher Owner s Manual And while wasn t able to locate a copy of the 1955 FM 40 schematic below is the text from an early 50s brochure for the FM 40 The eight tubes of THE FISHER Model FM 40 include four of the dual purpose type They are used in twelve individual stages a tuned two stage amp Separate local oscillator RF amplifier of the low noise cascode and soinn tiree TE eee a Tatio detector 4 cathode fol lower to assure low distortion and independence from output load charac teristics and cable length a meter circuit tube and a rectifier Figure 5 Fisher Model FM 40 Tuner Specifications 1951 1961 1961 1961 1962 196 1962 1962 1962 1962 1963 1963 1363 t9631 1564 First complete receivers with Multiplex First FM Stereo Multiplex tuners with STEREO BEAM First loudspeaker system with frameless woofer con liminating all parasitic resonance First internal switching system to permit immedi ate tape playback with use of all controls and switches First simplified operation Control Amplifier with in frequently used controls behing a front pane
3. had one I ve also heard the 500B s superior FM performance was attributed to it having up to 4 IF amplifiers and 3 limiters almost as many as the much more expensive FM 1000 tuner So let s debunk that while we re at it shall we Below is the chassis layout and stage labeling as found in the same 1962 Fisher 500B Service Manual TUBE LAYOUT V6 EMB4A ii TONE CHB hc CHA CH B CONTROL CHA PREAMP ve 12AX7 12AX7 12AX7 12AX7 ECC83 ECC83 ECC83 12AX7 a AU 010 ANP RF AMP a AND OSC MIX J6KC SYNCH OSC ECC83 ECC83 LOW PASS AND 19KC AMP ECCB81 12AT7 CH 8 VOLTAGE AMP AND mu yo CH A PHASE CH 8 PHASE INVERTER 12AX7 INVERTER ADJUST ECC83 ADJUST i i CH A POWER AMP CH B POWER A AP 59 Figure 25 1962 Fisher 500B Chassis Layout Count em two IF stages and 2 limiter stages So nothing here at least seems to substantiate the 500B s legendary FM performance don t dispute that it has excellent FM but it s not for the reasons so widely attributed Now there were significant changes in the up coming 500C tuner however am attempting to complete this summary as chronologically as possible so let s save the best for last and take a look first at what happened to the Fisher 800 model The 800B and the 800C were also major contributors to Fisher s reputation for superb stereo reproduction and AM FM tuner performance throughout the 1960s As we ve seen ear
4. 963 and they were soon to be joined by their lower cost baby sister the model 400 So how had these models changed with respect to their FM front ends Let s begin by looking at the 800C schematic Fig 28 Fisher 800C Sub Miniature Frame Grid Triode 6GKS5 front end ANYEMWA COMME TIONS Ca fz y2 ICD ECCHS GAGE Ve ve E 084 6808 Figure 28 1963 Fisher Model 800C Receiver with 6GK5 6AQ8 Non Cascode FM Tuner Front End Well there certainly was a change The all new tube in the 800C front end is using the sub miniature T5 6GK5 a single triode design intended as a low noise VHF RF amplifier This tube has a frame grid construction in a glass envelope but IS NOT a nuvistor as it is so often portrayed Its output is fed into the single 6AQ8 as oscillator IF amp What s very strange with the 800C is while no mention of this feature in the owner s manual there is often on some C models a small label on top of the tuner identifying the 6GK5 6AQ8 as Golden Synchrode yet there does not appear to be any sort electronic of rationale to justify that Since the 6AQ8 is nothing special does this mean Syncrode is just the inclusion of this new single triode front end Was this Golden Syncrode 800 BALANCE Figure 29 1963 Fisher Model 800C AM FM Receiver Not cascode but quite possibly synchrode whatever that is the last 800 model instead focused more on the whistles and bells such the automatic ste
5. EAD PREAMP LOW FILTER AMP HIGH FILTER AMP LOW PASS AND 19KC AMP 3 TE ECC83 ECC83 er 2100 12AX7 ECC83 12AX7 RIGHT PHONO AND TAPE HEAD PREAMP SERIAL NO EF94 EC97 6AU6 6GK5 va LEFT PHAS PHASE sai O 12AX7 LEFT DRIVER PHASE VERTER ADJUST DRIVER IN TO REVERS ona me L PUSH PULL IGH USH PULL OUT IN OUT IN AUDIO OUTPUT AUDIO OUTPUT SPACEXPANDER JACKS L 7591A L 7591A Figure 34 1964 Fisher 500C Chassis Layout serial numbers 30001 59999 inclusive So the final iteration of the famous Fisher 500 receivers chimes in with no less than 4 IF gain stages and 2 limiters Plus in an interesting twist the 500C front end appears to be a blend of the 400 s Golden Synchrode and the much more expensive FM 1000 tuner layout So would submit to everyone that THIS arrangement just might be the Holy Grail of Fisher tuners lt insert trumpets here gt All HAIL The 24 Karat Golden Synchrode So where am going with all this have absolutely no doubt that the Fisher FM tuners and receivers produced during the Golden Age of HI FI and had performance that represents some of the best that has ever existed My intentions for this article were simple and that was to better define what constitutes cascode and synchrode front end circuitry and to establish exactly which Fisher models used them Many of our members are spending large amounts of money purchasing these vintage receivers and t
6. In Search of the Golden Cascode Debunking The Myth of the Golden Synchrode By member callsign WopOnTour for the Rocky Mountain Radio and Audio Society believe that may need to clarify exactly what have been claiming at our most recent meetings and numerous subsequent emails with respect to inconsistencies that we ve all observed being said posted and published regarding the Fisher brand FM tuners and receivers equipped with so called cascode or Golden Cascode front ends With so many vintage audio experts out there in cyberspace contributing to the mass confusion in this regard it s time to set the record straight so to speak Many of you have requested my assistance in this regard which generated this article for our RMRAS newsletter So we might as well start at the beginning What s a cascode In vacuum tube electronics a cascode connection sometimes incorrectly called cascade is a gain stage where the cathode of a valve is directly connected to the plate of another valve This is typically done with triodes often using dual triodes housed within the same envelope This coupling may include a resistor capacitor or even an inter stage element such as a transformer or autoformer A cascode amplifier connection can also be created using a pair of solid state components such as BJTs or FETs aka a Darlington Pair Figure 1 is a typical vacuum tube cascode connection schematic as created by Tube Cad
7. M 200B i e a cascoded 6DJ8 twin triode combined with a pair of 6CW4 nuvistors albeit with additional IF stages gangs and limiter circuitry Figure 14 is the chassis layout for the venerable FM 1000 taken from a genuine Fisher Service Manual Figure 13 Fisher FM 1000 Tuner FM 1000 TUBE LAYOUT CATHODE FOUOWIR AND WU METER amr LOW PASS AND IRC AMP 5 Pe man jack 60J8 MICROTUME ANP ECCas 6BL8 OND eee Ane ECF80 T dij R215 12AX7 ECC88 Z7 vu FIED SHENGTH L296 oH METER ADJUST METER ADJUST STM MTER paiiar 30 F aH st Z3 istint Z4 mo Mien mp 0 pate ee eee 6AU6 EF94 I ave 6DJ8 ECC8E 4 6AU6 AUDIO iwo y os sn SE EF9o4 ac bled 6267 6267 Bees Golden Cascode EF86 EFS with Nuvistors OF 6DJ8 ECC8B INS 118 Figure 14 gt Fisher Model FM 1000 Tuner Golden Cascode Front End Golden Cascode Yes Golden Synchrode ummm No Not Quite Now while do not dispute the Golden Synchrode moniker had some sort of technical rationale within Fisher that might be reflected by these changes they apparently didn t choose to use the term themselves in much of their own marketing materials This is clearly evident by its strange absence within the ever growing list of Fisher Firsts found in almost each and every Fisher product owner s manual This one circa 1966 Figure 15 clearly identifies Fisher s pride in their cascoded front ends and specifically of the Go
8. NING INDICATOR poe VOLTAGE AMP 12AX ABOVE VOLTA LEFT PHONO ANO C7 5 V10 Tapt He HEAD PREAMP Ct ECC83 12AX7 12AX7 FCCE3 12AX 7 JRI v4 AND vs aTa AMP 2ND IF AMP NS im LIM RIGHT e v9 TAPE FEAD EOEOHOE PREAMP S f EC900 EC92 Ow 55 FAM EAUS LOW PASS bet AND I9KC AMP S4A5 6AB4 6BAE AND VRC AMP aves C R RIGHT DRIVER te DH DRIVER tee ates a 100 au TO 2 E 71 v3 LEFT Delve wis omy a makes Mey MAASE ge ECCS3 PHASE INY OSC Mix P 157 if AMP AX7 ECC83 ECC83 12 V101 f all i ECC z 17AX7 ea A 28K EUI pa Os osc i j ried 7 Qro ECC83 EAA E I12AX7 sUDIO am 12AX7 AUDIO AMP e LEFT PUSH PULL AUDIO RIGHT IS AUDIO LEFT ah ene AUDIO RIGHT PUSH PULL AUDIO RIGHT 4 LEFT RIGHT sr LEFT UTPUT OUTPUT CSCS UTPUT r ar LEFT CGS ED ICL V14 V1I5 V16 V17 Out IN OUT IN OUT IN OUT IN TO REVERS SERIAL NO TO REVERB L 7868 ae 7866 re SPACEXPANDER JACKS Se 9858 ead Sa ee ee SPACEXPANDER JACKS Early Model Fisher 400 Receiver Chassis Layout Late Model Fisher 400 Chassis Layout Figure 32 Comparison of Chassis Layout Fisher Model 400 Early Late Production So the later model 400 displaced the 6H56 and added pare of 6AU6 in its place stretching out the tuner to create an additional 4 IF amplifier and a second limiter which no doubt came with an improvement in FM performance The Fisher King The 500C So that
9. Surprise The vaunted 500B so usually associated with unrivaled FM performance that s often attributed to it having the Golden Cascode front end actually used a single dual triode In this case the 6AQ8 is connected in typical RF amplifier fashion with the second stage of the amplifier mixer using a more conventional grounded cathode plate follower arrangement Unlike the previous models could find no Fisher marketing materials stating the 500B used Golden Cascode and likely for very good reason It didn t have one Now just for my amusement let s compare that to the 1961 Harman Kardon TA260 front end as most of you know I m a huge H K fan 1961 Harman Kardon TA260 Receiver FM Front End Dual Twin Triode with AFC a Vic V2 ECCRS EACGS CC85 6A08 Figure 24 1961 Harman Kardon Model TA 260 Festival II Receiver FM Tuner Front End So the H K receiver isn t using a cascode RF amplifier either But as one can see it is very similar to the Fisher 500B A single tube grounded grid RF amplifier feeds into the conventional plate follower at the mixer oscillator much like the 500B however with an additional triode sandwiched in between consisting of its Automatic Frequency Control AFC circuitry My point here is that the H K receiver s front end really isn t that different from the 500B This despite all too often being referred to as inferior in design to the 500B s cascode front end which might make sense if it
10. brings us finally to the venerable 500C that a great many claim has the ultimate in tube based FM circuitry and the pinnacle of Fisher tube based receiver technology Figure 33 is the schematic for a 1964 Model 500C 1964 Fisher Model 500C Receiver with Golden Syncrode and nuvistors ANTENNA CONNECTIONS czo j RAG o idd i j L Si SECTION 4 FRONT So Oe a Figure 33 1964 Fisher Model 500C Receiver with Golden Synchrode 6HA5 6CW4 Nuvistor Front End Based on this diagram it should be clear that while this obviously isn t a Golden Cascode it does appear based on what we ve learned about the model 400 to have some the characteristics of the so called Golden Synchrode and I m very tempted to place a symbol here but now with potential performance improvements thru the use of nuvistors in the front end In the 500C the antenna connection into the tuner is greeted by an EC900 6HA5 which is a 7 pin sub miniature VHF triode with a twinned cathode connection and an internal shield connection The V1 plate in this case is inductively coupled both to the grid of V18 6CW4 nuvistor thru the inter stage relationship between RF coils L2 and L3 as well as the grid of V2 nuvistor through L4 Z1 then couples the connection to V3 the 1 IF amplifier a GHR6 yet another T5 sub miniature tube they were in vogue after all but this one a sharp cutoff pentode LEFT PHONO hi LEFT AND RIGHT LEFT AND RIGHT TAPE H
11. d in this article please feel free to contact the writer at wopontour gmail com Enjoy Your Vintage Audio
12. dGeem Wiyot 3 ar T 4 12 TERMINAL GUID POWDERED IRON Er T of HST POINT nro Se s o JO Figure 22 1960 Fisher 500S FM Tuner Front End So can you find the cascode connection No Well neither can That s because the front door s 6AQ8 triodes are not connected in cascode but a more conventional less complex and perhaps less expensive single tube RF amplifier mixer combo In short the 500S is NOT a cascode front end THE FISHER So what about the other great Fisher stereo receiver models that appeared over the period of the next 5 6 years or so often considered to be the Golden Age of audio in America Were they ALL Golden Cascode Golden Synchrode Something else Let s begin with the venerable 500B None would dispute the 500B was THE FM stereo receiver that launched a very dominant period for Fisher in the home audio marketplace The 60 watt 500B didn t have an AM tuner Fisher faithful would say that was to make room for the multiple IF stages and full MPX stereo and massive transformers As such it s widely assumed published and stated that it was equipped with the Golden Cascode front end Below Figure 23 is the schematic from the genuine 1962 Fisher Service Manual for the 1962 model 500B serial numbers 20001 39999 1962 500B Dual Triode front end L6 Where s the Cascode Figure 23 1962 Fisher Model 500B Dual Triode Non Cascode FM Tuner Front End Surprise
13. heer g Tote Fiest FM Tuner te Crevil for high Fouro ode Coins dence Liou 966 First ali transiss Proteclice So despite these Fisher Firsts acknowledging almost every nuance in Fisher technology why is there no mention here of the 1963 Golden Synchrode Who knows perhaps it because it wasn t a Fisher First personally find that notion doubtful however could it be because the term synchrode isn t even in the dictionary That brings us now to the infamous Fisher FM receivers that began appearing in the late 50s How did these developments in front end technology affect the value leaders of the Fisher line up Enquiring minds want to know So let s begin with the TA series that pretty much started it all beginning with the original 500 600 and 800 models Not to be confused with the B and C models that followed them these initial receiver models usually had a TA prefix in their chassis labeling however they were seldom marketed or referred to as such more often just The 500 or The 800 None of them had true MPX FM stereo although the TA600 and TA800 did come equipped with an MPX output that could be connected to a separate MPX adapter to gain that capability The original model 500 Figure 16 was not a stereo receiver it was monophonic Figure 16 Fisher Model 500 AM FM Receiver But it had both AM and FM capability AND as one can see from its front end schematic Figure 17 a cascode FM f
14. heir enjoyment is certainly enhanced by getting exactly what was expected My goal was to educate to the level necessary to make informed bidding and or purchasing decisions when buying these items on line and during local equipment swap meets and ham mer fests And now my disclaimer Now as everyone that s ever tinkered with vintage audio circuitry or even more seriously as a service technician will tell you that manufacturers OFTEN made running changes to their circuitry design and or component compliment Additionally there were often numerous data errors and false information spread by the marketing channels in the form of magazine and catalog advertising Combine that with unintentional human error made during schematic creation in aftermarket service products such as NRI schematics and SAMs folders makes for all sorts of variables that are just out of my or anyone else s control Thus it makes nailing down empirically exact and 100 reliable data specifications information and schematics a near an impossible task even today let alone for an era that was nearly 50 years ago However I can tell you that have compiled this information with only the best intentions using the most reliable information available and to my disposal but make no absolute guarantees as to its accuracy That being said if anyone has data that might add to or supplement what have done here or that even absolutely conflicts with the content as state
15. interesting trivia nonetheless 1960 Fisher i Model TA800 FM FM RE AMP Golden Cascode 1 EECRE amp wie Front End 170 24mm 155 EXT FM ANT 5y pov ere 5 3 y TERM BOARD 1 zmir mnt ommi 2Y She f i i I i i l I I i i l 1000 gt gmint Re S T NPO H 5mmf l Armm N750 KPO T yh JUMPER GIMMICK Figure 20 1960 Fisher TA800 FM Cascode ECC88 Front End In late 1960 Fisher updated the 500 to the 500S S for Stereo and it joined the existing stable of TA 600 amp 800 receivers Like the TA models it was AM FM shared the polished brass plated faceplate and like the 600 was equipped with a quad of 7189 output tubes the earlier 500 mono used KT66 or EL34 depending on model year however was now rated at 5 watts higher 45wpc vs 40wpc than the TA600 Figure 21 1960 Fisher Model 500S AM FM Receiver 45 wpc The 500S is in many ways quite similar to the 600 however it had solid state voltage rectification the 600 used a pair EZ80 rectifiers and revised chassis layout with slightly smaller transformers However another difference was its FM tuner front end looking at a schematic of the FM tuner used in the 500S Fig 22 oe 6 ee OOS EO OO amp njettess oace Pnad Wilson ss i a ee e en eE i Seen TE Q 00 reat MSs 200 pet ae sf K3 E jani i i pry TERMINAL GW s4 L
16. ity sensitivity and rejection of unwanted signals Three wideband IF Stages are used followed by a ratio detector that is linear over an extremely wide range The multiplex converter is the superior time division type utilizing two balanced diode bridges and a 38 ke synchronous oscillator acting together as electronic switches This circuit reduces noise and distortion to the theoretical minimum and achieves the greatest possible stereo separation The famous STEREO BEAM indicator signals instantly whenever a station transmits a multiplex stereo program Figure 30 1964 Fisher Model 400 Owner s Manual Introduction Now let s look at the 1964 Model 400 schematic shall we 1964 Fisher Model 400 Receiver FM Front End SWHCH POSITIONS 1 s s3 s4 5 PIO34 3 FM FRONT END tare f mice couparss selecte MOKITER tnter f comtous SPEAIER A st Hd su su ATT TT A eT TC RD Sea eT Is this a LES AS A A E LN ae ae Ve a stretch aan pt ope ALi SLICES aR SKONE J TRE N 1 POSITION ANTENNA CONNECTIONS ic c 3 S SECTION 2 FRONT Figure 31 1964 Model 400 Receiver FM Front End Schematic late build serial number 48001 and up The first thing you notices is the 1 tube has been changed to a 6HAS sub miniature T 5 single triode tube with electrical characteristics and stature VERY similar to the 6GK5 used in the 800C The next tube is an EC92 6AB4 single triode also sub mini as the oscillator mixer and eventua
17. l cover yet immediately accessible ba loudspeaker with eddy current damped voice coil First bass speaker with combined serrated alumi num and fiber cone First FM Tuner Kit with separate d Arsonval meter for tuning and separate cathede ray stereo broad cast indicator STEREO BEAM First Stereophonic FM Tuner with TUNE O MATIC Motor Tuning First Supersonic Wireless Remote Control in a high fidelity component First to use 8417 tubes with unique cavity anode design First power amplifier to use oscilloscope type fre quency compensated input circuit First amplifier kit with STRATABALANCE visual dy namic balancing system First multiplex adaptor with flywheel synchroniza tion Closely approaches theoretical limit of noise rejection and of all spurious responses First AFC with strong locking on weak signals with no pull in from adjacent strong signals In just a few years Fisher s more advanced FM tuners such as the FM 60 or KM 60 Strata Kit version and the MPX stereo FM 100 were also equipped with a cascode front end and was dubbed the Golden Cascode by the Fisher marketing machine They even silk screened the moniker directly onto the tuner chassis adjacent to V1 Figure 6 Fisher Model KM 60 Tuner Chassis Markings Note that in these tuners the Golden Cascode front end is the frame grid 6DJ8 ECC88 tube and V2 is the 6AQ8 ECC85 oscillator mixer not technically part of the cascode co
18. lden persuasion but absolutely no mention of synchrode golden or otherwise So if the use of nuvistors post cascode does not constitute a Golden Synchrode then exactly what does FISHER FIRSTS Milestones In the History of High Fidelity Reproduction oy Pivet high fidelity sound ayslams feabeting a basm power amplifier inverse leedback accuatic speaker compartments infinite baffle and bass reflex anc magnetic cartridges eoyFirst exclusivety high fidelity TRF luner festuring broad luning 20 20 000 crcle fidelity cayFicst twoeunit high fidelity system with separate spenater enclosure jqaeFirst conzial spoakor system ooeFirst high fidelity tuner with amplified AVC 999First ynamio range expander o99First eway speaker in a highelicolity system Qa0 First center of channel tuning indiestor 425Firat preaesplifier aqualizer with aalective phans graph equalizalion soeFirst dynamic range expandor with feedback jooFirst FM AM tuner with variable AFC qo First S0 watt all triode aemoplifier so F iret soll powered master sadio control gti First selt powered anecwenre sharp cviott filer syne tem for high fedelity us osoFirat unteeraal harn type apeaker anclesure for any room location and any spenker jocoFirst FM AM receiver with a cascode front and Pa A a ee ee 981Firat low cost laconic mixer fader rooeFirst maderately priced professional FM tumer with feo meters ossFirst peak
19. les adapier with STEREO BEACON and automalic switching mons to stereo Sti First compiole FM multiplex stereo receivers 1061First FM storeo tuners with STEREO BEACON and STEREO BEAM PO First elernal switching system to persit immediate iape OlayDack with vse cf all controls and switches votive Figure 15 More Fisher Firsts Taken from a 1966 Fisher Owner s Manual jenFirst simplifiad operslion conirobamplifier frequently usod controis behind fronbpane yot immediately accessible ef is62Firat Joudapeaker with ecdy current caseec ence Cor ognFirat FM tuner kit with separate CAreceen meee for tuning and separate calhoce rey meno Sees casl indicator STEREO BEAN oGaFirst power amplitiar te use cecilioscope tee Qvency compensaiod input circs ond Fiest amplifier kit with STRATABALANCce cynamic balancing system First multiplex adapter with Gon Closely approaches theare vor rejection and cf all sparous rest pcrpes 904 First FM Stereos Tuner with STER soiFrst poripherally driven tweeter ect dome oe4Fiest to wse TUNE O MATIC tuner 1265 First Abl ay One All Transia i965 Fest F E T front end desion w Avigsmatc Gain Co trol ol the best prior so 7566 First FM tener with Acto Attenuator 056 Firat FM tuner ic achieve O limes Detter than the bes prevo r56 First FM Turer 3o use a 80 Detector eliminat ng all cistorman z tuner 1365 First FM Tuner with C
20. lier the first generation model TA800 used a Golden Cascode FM front end So can we assume this continued Let s take a close look under the hood of the 1962 Fisher SOOB Figure 26 is the front end schematic for the Fisher model 800B serial numbers 10001 19999 Fisher 800B Twin Triode Front End VI 8 cis RISO ate cis CI7 cig Suut A KS C2 33 uuf C27 iOOuuf L7 R29 na 68uH ISOK T an loar 18V OTESTPOINT 1 Rae Figure 26 1962 Fisher Model 800B FM Front End Fisher 500C Service Manual for serial numbers 10000 19999 Look familiar Again no cascode and in fact the circuit is nearly IDENTICAL to the 500B However while the 500B also had 2 IF stages this 800B has only a single limiter circuit This was most likely due to the lack of real estate on the chassis Fig 27 given that the 800B also had AM radio unlike the 500B Note the twin EM84A magic eye tuning tubes v9 AM TUMING miOIC Aloe tmrbae i TUNNG INDICATOR j rayi rOCan ECCEI IIAN iita A G Lechas taax anv ecces Wi4 D z Po SH vtot ons ins aw tf aa am CONVERTE vs gO ne rrr Pe o W 1 Sanaa yo vai J CH browse amr de CHA La sais Figure 27 1962 Fisher Model 800B Chassis Layout Well OK then We ve established that the 500B and 800B receivers were virtually identical with respect to their FM front end arrangement But the final versions of these models the 500C amp 800C began appearing late in 1
21. lly coil coupled to the grid g1 of an EF93 6BA6 pentode which represents the 1 of 3 IF stages But apparently the use of this single triode as the V1 point of entry IS according to the owner s manual Fisher s Golden Synchrode how anti climactic Nuvistors apparently had nothing to do with it About all can glean that s special about this circuit is its unique use of a pair of single triode tubes inter stage coupled and guess a somewhat loose assimilation of a cascode like connected circuit represented by the plate of the EC92 and the cathode of the EC93 coupled via the Z1 coils the chrode of synchrode Figure 18 Fisher Model 400 Chassis Photo With Golden Synchrode Could this be Fisher s ONLY receiver with Golden Synchrode Well the similarities between the 400 and the 800C lead me to ascertain it too was Golden Synchrode even though there doesn t seem much from Fisher to support that It should also be noted that while this was the latest wiring schematic for the model 400 that was able to obtain from my archives for serial numbers 48001 and up looking at earlier model 400 schematics that have however there were only minor circuit differences in the front ends while there were much more significant changes both tubes and arrangement further downstream in the tuner see Figure 32 V6 Y7 LEFT AND RIGHT EMB4A O EMB4A TONE CONTROL LEFT AND RICHT aie TUNING INDICATOR TONE CONTROL LEFT AND RIGHT ECCB3 TU
22. nnection Unfortunately did t have a full schematic for the FM KM 60 however here is the schematic for the slightly later FM 100B model clearly showing the identical cascode 6DJ8 configuration Fisher 100B Tuner 4 V2 A ECC88 6Du8 c l 1 2 ECC85 6AQ8 1000 PF Cascode Front End FM ANTENNA S C20 TEST POINT K i A Figure 7 Fisher FM 100B Tuner Front End Schematic In fact even the venerable stereo FM 200 model used the exact same 6DJ8 as its Golden Cascode cs a9 c 10 1000 R4 RG 100K 120 Figure 8 Fisher Model FM 200 with Golden Cascode and even its chassis was labeled as such Fig 9 Figure 9 Fisher Model FM 200B Chassis Markings However when looking at the FM 200B tube layout Figure 10 taken from a genuine Fisher service manual it clearly shows that the signal entering the 6DJ8 Golden Cascode tube was eventually piped into a pair of 6CW4 Nuvistor miniature tubes Fisher FM 200B AAFS ona Golden Cascode 6CW4 Nuvistors Figure 10 Fisher FM 200B Chassis Layout from Fisher Service Manual Looking more closely at the schematic for the FM 200B Figure 12 one can see that while the cascode RF amplifier is maintained the oscillator and mixer has been revised to include a pair of 6CW4 nuvistors Nuvistors are highly integrated tube electronics housed within a small thimble sized metallic envelope In a sense nuvistors represented the bridge between
23. power indicator in high fidelity i955First master audio contro chassis with iive position Mixing facilities 1955First correctty equalized direct tape mead preampii fier with selt powered master audio control COPYRIGHT 1566 FISHER RADIO CORFORATIC A AIT Rights O66First alltransistor oroamoplifier equalizer First dual dynamic limiters in an EM tuner for home use OS1F irst performance monitor in a high quality ampliier SouFirst FM AM tuner with two moters Ss First complate ene feaponee curve Indicator for bass and treble oo7Fires GOLDEN CASCODE FM boner porFirat Mierohay tuning indicator jQiaFivat atereogheric radic phomograph with magnetic slerco cartridge 950First high quality remoto control system i959Fisgt Gamplele steoreophenic PM AM receiver FM AM tuner avdio control 40 walt amplifier 1959First high compliance plus high efficiency Free Pis lon lcucspesker system 1960Fisst lo use MicroRay ror fa tuning ond as a record ing audio lewal indicats owSaaithsoanian Institution Washington D C receives for its collection America s firat comeaserciaily maru faclured High licelity radio phonagraph mode by Avary Fisher in 1937 BSOFirst reverberation davice dor vse in high tigellty equipment che Fisher Dynamic Spa cexrpander 1980F irst stereo tuner with MicroTunme so0F iret front panet antenna selector switch 72 300 ohm Leeal Distan oositions fei Firat FM Slarea multip
24. r with meters First Peak Power Indicator in high fidelity First Master Audio Control Chassis with five position mixing facilities First correctly equalized direct tape head master audio controls anc self powered preamplifier First to use Power Monitor in a home amplifier First All Transistorized Preamplifier Equalizer PRINTED IN U S A 1956 1956 1956 1956 1957 1358 1959 1359 1959 1960 1960 1960 1960 1960 1960 1960 1960 1961 First dual dynamic limiters in an FM tuner for home Use First Performance Monitor in a high quality ampli fier for home use First FM AM tuner with TWO meters First complete graphic response curve indicator for a pee and treble 1 l icrokay Tuning Indicator First Stereophonic Radio Phonogreph with Magnetic Stereo Cartridge First high quality Stereo Remote Control System First complete Stereophonic FM AM Receiver FM AM tuner audio control 40 watt amplifier First high compliance plus high efficiency free piston speaker system First to use MicroRay for FM tuning and as a Record ing Audio Level Indicator First complete stereo FM AM receiver with 60 watt power amplifier and new 7591 output tubes Smithsonien Institution Washington D C accepts for its collection America s first commercially man ufactured high fidelity radio phonograph made by Avery Fisher in 1937 First reverberation device for use in high fidelity equipment The Fisher
25. reo beacon needle type signal tuning earlier models used magic eye tubes and improved tape and phono input features But the fact remains is the only Fisher 800 model that used cascode was the original early 60s TA800 model So just what WAS synchrode As previously mentioned there appears to be no amplification term or definition within the realm of electronics that seems to allude to it But as far as I ve been able to ascertain the actual term Golden Synchrode made its first appearance with the launch of the 65 watt MPX equipped Fisher Model 400 sometime late in 1963 Model 400 production continued through to the end of Fishers tube era with numerous running changes without a model designation suffix change taking place over the following year or two Below is an excerpt from a 1964 owner s manual for the Fisher model 400 Fig 30 THE FISHER 400 STEREOPHONIC FM Multiplex Receiver y NEW FISHER 400 incorporates on a single chassis a highly sensitive FM multiplex tuner a Master Audio Control with a full complement of controls and features and a dual channel 65 watt power amplifier with ample reserve power for full room volume with any pair of loudspeakers Many new advances in the technology of music reproduction have been included in the 400 design The front end for example is of the new FISHER Golden Synchrode design employing a specially developed RY amplifier combined with three tuned circuits for maximum selectiv
26. ront end capacitor coupled Original Fisher Model 500 asue gt 7 F Figure 17 1957 Fisher Model 500 FM Receiver Front End Now comparing that to the front end schematic Fig 18 for the 1960 model TA600 a single 6AQ8 tube is now used both for the RF amp and the oscillator mixer front end The cascode connection within this triode is especially obvious due to the way the schematic more correctly aligns the cathode above the plate much text book discussion of cascode tubes often refers to the upper and lower triode within the circuit Fisher TA600 Cascode FM Tuner Front End 1 2 ECCBS 6A08 e Vi amp 1 2 ECC85 6AQB 4 i t i t I l l C C145 A x f V2 8 1 2 ECC85 6408 m m e e e e e e A E Figure 18 1960 Fisher Model TA600 FM Cascode Front End Schematic So what about the top of the line Fisher 800 model The TA800 was often the only Fisher receiver advertized back in the early 60s as employing a Golden Cascode tuner Here s a copy of a Fisher 800 ad from the 1961 Radio Shack catalog Fig 19 An adjacent ad for the model 101 R tuner isalso shown Golden Cascodes for all Fisher 800 Stereo FM AM Receiver An Engineer s Dream Only 19 Monthly e 60 Distortion Free Watts 429 Twenty four Controls The most sensitive and most powerful stereo receiver in existence Every single part designed and selected as if it were THE most important part Hum and noise i
27. rried a reputation for superior FM performance Figure 2 is the cascode connection at the RF amplifier front end of an H H Scott model 310 FM tuner note the 300 ohm antenna connection to the grid of the 6BS8 triode While it is coupled by a 0O1uf capacitor the plate of the one half of the 6BS8 is clearly connected to the cathode of its other half the 6BS8 is a dual triode The amplified signal would then continue on to a 6U8A triode pentode which acts as the oscillator mixer Figure 3 H H Scott FM Tuner circa 1959 The 1st generation H H Scott tube tuner designs incorporated the 6BS8 RF amplifier and 6U8A oscillator tubes housed within a modular Silver plated tuner assembly All early H H Scott FM tube tuners with few exceptions used this Scott standard 2 tube Cascode FM front end which was sometimes referred to as the Z FM 3 assembly Early H H Scott receivers such as the model 340 also used an identical cascode arrangement As an aside note H H Scott eventually went to compactron tubes in their front end s RF amp 6M11 and eventually like many manufacturers condensed form factor nuvistors The point here being cascode and nuvistor front ends were commonly used by manufacturers other than Fisher The circuit schematic not the tube itself will be required to determine this To get to the bottom of GOLDEN cascode however find we must start with Fisher s stand alone tuners Early Fisher FM tuners monophonic al
28. s completely inaudible Fifteen input and out put connections for every stereo and mono program source and application including center channel multiplex tape monitoring Plus Four Diodes A36CKX715 Ship wt 40 Ibs 19 Monthly Net 429 50 Tab a pss Leal a Pa aa at her 101 R Gold Cascode FM AM Tuner first Gold code Stereo Timer Automatic n ppi ian oe en flywheel tuning 4 IF stages Hee eee Sah gain and bandwidth with minimum distortion Only 9 50 Monthly z gain control noise and hum are inaudible Low eek we a audio output stage allows use of cables to 30 IO 50 no loss of signal 4 controls Seven outputs Cross pe BE h hle Fifteen tubes 2 diodes Size 15 x R amio s e aa ii e Ea E R a Only 9 50 Monthly Net 229 50 Bei Aes i Figure 19 Fisher TA800 Advertising Ad Radio Shack Catalog 1961 And following up with Figure 20 the schematic for the original 1960 Fisher model 800 the TA800 Yes we find the classic Golden Cascode ECC88 6DJ8 into an ECC85 6AQ8 mixer oscillator Remember the FM 100B tuner As an interesting aside note the TA800 was also equipped with a small blunt cut wire antenna connected to the grid circuit of the mixer that apparently was to act as some sort of noise cancellation device that improved reception the item labeled simmick in this schematic from SAMs folder 530 5 can find no reference as to the true performance significance but
29. so used a cascode front end dating all the way back to the early 50s as shown in this list of Fisher Firsts Fig 4 gleaned from almost any Fisher owner s manual Another copy of which we l discuss in more detail a bit later in this article 1937 1937 1337 1338 1938 1939 1939 1945 1346 1949 1952 1952 1953 1953 1953 1954 1355 1955 1955 1956 1956 1064 FISHER RADIO CORPORATION FISHER FIRSTS Milestones in the History of High Fidelity Reproduction First high fidelity sound systems featuring a beam power amplifier inverse feedback acoustic speaker compartments infinite baffle anc bass reflex and magnetic cartridges First exclusively high fidelity TRF tuner featuring broad tuning 20 000 sete fidelity First two unit high fidelity system with separate speaker enclosure First coaxial speaker system First high fidelity tuner with amplified AVC First 3 Way Speaker in a high fidelity system First Center of Channel Tuning indicator First Preamplifier Equalizer with selective phono aph equalization irst Dynamic Range Expander with feedback First FM AM Tuner with variable AFC First 50 Watt all triode amplifier First self powered Master Audio Control First self powered electronic sharp cut off filter system for high fidelity use First Universal Horn Type Speaker Enclosure for any a location and any one j t ron f First moderately priced professional FM Tune
30. vacuum tubes and solid state transistorized circuits One of their first applications besides military was in FM tuners due to their VHF capability temperature stability low noise and smooth linearity Figure 11 RCA 6CW4 Nuvistor Tube Courtesy National Valve Museum So was THIS the infamous Golden Synchrode then Hard to say being that unlike cascode there appears to be no known definition for a synchrode connection in any electronics texts that could find Try plugging the word synchrode into a search engine and see what you get But what we do know is this basic point of entry configuration is what forms the initial building block of the synchrode front end More on that in a bit However to this point in time circa 1960 61 the cascoded 6DJ8 front door is clearly still being referred by Fisher as Golden Cascode j w Nuvistor ee a Kewe ra Figure 12 Fisher FM 200B with Golden Cascode and Nuvistor Front End So the use of nuvistors combined with a Golden Cascode appeared to be destined for even more expensive broadcast quality FM tuners such as the FM 1000 which is often described in vintage audio circles as having Golden Synchrode Whether that is true or not depends on who you talk to but just one of the many myths this paper attempts to debunk What we know as fact is the rare and desirable FM 1000 used the exact same 3 tube configuration in it s front end as the aforementioned F
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