Fender 5D6A Find

[plexi50]

Just aquired a 4x10 5D6A without the speakers. Have 2 of the jensen bell covers. Tube chart perfectly intact. Im starting to get sick to my stomach. Same customer from last night on the 1959 5E3. I noticed when i was blowing it out that it has two 5U4 rectifier tubes. All tubes are CBS. Face plate lettering is very good. What the hell is going on here? He says he has more as well later.

[HotBluePlates]

And why is the tweed ripped off all of them? 

[plexi50]

Not a clue on the missing tweed for last 3 amps i have had here. I didnt own that Super Amp but i sure as H own these. I feel quilty all of a sudden. My friend found a 1966 Princeton 3 months ago painted blue and pink. Go figure. Is this amp a more desirable one? Have never own either of these amps.

[HotBluePlates]

It would be among the first narrow-panel Bassman amps. Strangely, we don't have a schematic for it on the site. It would be interesting to get you to compare it to the 5E6 Bassman schematic to see what the differences are.

Every tweed Fender is gonna be desirable to some degree. I think folks are a little too fixated on the 5F6A, but that may be largely an issue of tinkering tone circuits until Fender landed on what players liked best.

[plexi50]

I would be among the first narrow-panel Bassman amps. Strangely, we don't have a schematic for it on the site. It would be interesting to get you to compare it to the 5E6 Bassman schematic to see what the differences are.

Every tweed Fender is gonna be desirable to some degree. I think folks are a little too fixated on the 5F6A, but that may be largely an issue of tinkering tone circuits until Fender landed on what players liked best.

Found schematic online. Was sorta hard to find it.

[sluckey]

.

[Geezer]

First glance looks pretty much the same as the 5E6

Cathodyne inverter.......and 12AY7 in V1 & V2, dual recto, 10Meg local feedback....wow, 2 gain stages, CF, then another gain. I'll wager that thing rocks!

[drgonzonm]

thanks for the schematic.  
 
I have speculated what the the circuit looked like.  

Any word on what the transformers and choke are?

FYI,  There was an individual who was making a copy of the 5D6 based on chassis #0035.  adding some extras calling it a 5D6B.  the amps were retailing in the $2000 neighborhood.  

Given the rarity of the amp, can you verify the PI.  

[punkykatt]

Plexi, once you get it up and running, it would be nice to see some voltage readings. Man, you got all the luck. Great deals you`ve had lately.

[plexi50]

Plexi, once you get it up and running, it would be nice to see some voltage readings. Man, you got all the luck. Great deals you`ve had lately.

Yes i will make note and supply you with the voltage specs. I have tested all the tubes and they are very good. CBS BP 6L6GC's. Power transformer is working. Filament voltage is good. B+ is 440VDC from rectifier with no load. Standby switch bad. Bypassed and no plate voltage through OT. Suspect choke. Will jump with 500 ohm resistor tommorow and see after checking choke. Might check tonight if i can catch my breath. Im wiped/

[HotBluePlates]

Standby switch bad. Bypassed and no plate voltage through OT. ...

The standby switch appears to have a cap to ground, according to the schematic. Don't know if it's present in your amp.

If it's there, that cap might be leaky and dragging the voltage down. Try unsoldering at the switch itself.

[plexi50]

Standby switch bad. Bypassed and no plate voltage through OT. ...

The standby switch appears to have a cap to ground, according to the schematic. Don't know if it's present in your amp.

If it's there, that cap might be leaky and dragging the voltage down. Try unsoldering at the switch itself.

Yes i was looking at that. The cap is present. There is no continuity on standy with DVM in either position but are going to there respective points in the circuit. Also it would have helped if i had looked closer at the PS caps. Removed tham and tested on analog. Dead saturated shot. The choke is measuring 61 ohms. 

[HotBluePlates]

The choke is probably fine.

[TIMBO]

YEAH, you guy's seem to snag all the good finds.

Just slightly off topic, the "cathodyne inverter" if i have got it right is in a lot of fender amps and not something new, any fors and against useing these inverters. They seem to be in alot of the early models and LTPI are more common these days.
Also with a 12A_7 PI drawing ~10mA of current, what would this type of inverter likely to draw in the current department.Thanks

[Geezer]

http://www.valvewizard.co.uk/cathodyne.html

Some info on the cathodyne. Merlin has info at the end on how to improve performance (not recommended in a vintage amp, but helpful in a new build). There is even more info in his new preamp (second edition) book.

[plexi50]

Man i bet this thing rocks too.  Werent we disscusing this amp a few months ago in another thread? Something about the differences if any in the 5D6 & 5D6A?

[Geezer]

Man i bet this thing rocks too.  Werent we disscusing this amp a few months ago in another thread? Something about the differences if any in the 5D6 & 5D6A?

Well then, let's discuss some more rare birds, then maybe more will turn up! 

[plexi50]

Back from Dr Extraction place. Going to take the best detailed pics i can get from my camera. I think the PI was of main concern but will get the preamp as well to see if it matches the schematic. Back in a bit/

[plexi50]

Ok. Here is part verification as to what is in my 5D6A. Let me know if i missed something.

Pics from top to bottom seperated are:
PI V3
V2
V1

[DummyLoad]

PI seems odd...

[plexi50]

PI seems odd...

Both resistors are color banded 51K. No color fade on this end. One reads 54K & 55K
There in circuit so that sometimes makes readings off a hair. 51K is an odd number. Maybe they are or were 56K and mis printed.
Even so the resistor would drift up in value instead of lower in value i think

[drgonzonm]

Man i bet this thing rocks too.  Werent we disscusing this amp a few months ago in another thread? Something about the differences if any in the 5D6 & 5D6A?

Again I post, that for those interested in the 5d6 circuit there are disassembly drawings of a 5D6, (sometimes referenced as a 5d6 DL), Some of the obvious differences are:
1.   the location of the 100 ohm resistor on V2 tube between the two plates.  the 0035 has the resistor on the board rather than on the tube socket.
2.   Rectifiers are 5y3's rather than 5u4's
3.   The transformers are 7926, 2770, and 14560 for the p/t, o/t and choke respectively.  
4.   The p/t reportedly does not have a bias tap, but has a 100 ohm resistor from the opposite HV secondary
5.   B+ voltage about 400
6.   The p/t is apparently small enough that the paper separating the windings is discolored, (I interpret this as a high sag application)

I am in the process of reviewing the pictures to identify resistor values. (To me its a slow process, since I keep forgetting the color codes.  Once I am done, I will post the layout and schematic on this forum.

Comparing the 5d6a circuit and the 5e6a circuits, I noticed three resistor value differences.  
1.  on the bias circuit 6800 v. 3300 upstream of the diode.
2.  on the bias circuit r-c ground, 47k v. 56k.
3.  On the cathodyne PI, B to plate 47k v. 56k.  

Without knowing what transformers are included on the 5D6a, the numbers above appear to be meaningless.  

Web page showing 5d6 disassembly:  steelguitarforum.com/viewtopic.php?p=1397040

[plexi50]

Pics of any and all part numbers. Chassis code matches tube chart numbers. The only numbers on the OT are shown. The PT has faint and hard to read codes. The logo has disintergrated from the top of the PT. I assume TRIAD? The choke has no numbers period. The tube sockets have etched script for the tubes used in the preamp,power and rectifier tubes on the chassis.

The preamp tube arraingement is in reverse on the etched script on the chassis from the tube chart.
Chassis etching = 12AX7-12AY7-12AY7. Tube chart = 12AY7-12AY7-12AX7

This had to have been done when it was being designed. I cant picture anyone even being able to see the etching unless you had the chassis out of the cab and on a bench

[plexi50]

Man i bet this thing rocks too.  Werent we disscusing this amp a few months ago in another thread? Something about the differences if any in the 5D6 & 5D6A?

Again I post, that for those interested in the 5d6 circuit there are disassembly drawings of a 5D6, (sometimes referenced as a 5d6 DL), Some of the obvious differences are:
1.   the location of the 100 ohm resistor on V2 tube between the two plates.  the 0035 has the resistor on the board rather than on the tube socket.
2.   Rectifiers are 5y3's rather than 5u4's
3.   The transformers are 7926, 2770, and 14560 for the p/t, o/t and choke respectively.  
4.   The p/t reportedly does not have a bias tap, but has a 100 ohm resistor from the opposite HV secondary
5.   B+ voltage about 400
6.   The p/t is apparently small enough that the paper separating the windings is discolored, (I interpret this as a high sag application)

I am in the process of reviewing the pictures to identify resistor values. (To me its a slow process, since I keep forgetting the color codes.  Once I am done, I will post the layout and schematic on this forum.

Comparing the 5d6a circuit and the 5e6a circuits, I noticed three resistor value differences.  
1.  on the bias circuit 6800 v. 3300 upstream of the diode.
2.  on the bias circuit r-c ground, 47k v. 56k.
3.  On the cathodyne PI, B to plate 47k v. 56k.  

Without knowing what transformers are included on the 5D6a, the numbers above appear to be meaningless.  

Web page showing 5d6 disassembly:  steelguitarforum.com/viewtopic.php?p=1397040

100K Ohm on V2. I think a year or so ago Steve told me not to handle or play with the Selenium rectifier too much. I have to read up on selenium and see what selenium really is. Might be good with captain crunch!

[tubeswell]

Any word on what the transformers and choke are?

I'm guessing the choke is DC rated for 200mA. Same with the HT winding on the PT. Just guessing.

[DummyLoad]

This had to have been done when it was being designed. I cant picture anyone even being able to see the etching unless you had the chassis out of the cab and on a bench

maybe this one was a prototype?

--DL

[plexi50]

This had to have been done when it was being designed. I cant picture anyone even being able to see the etching unless you had the chassis out of the cab and on a bench

maybe this one was a prototype?

--DL

Thats what i have been thinking. The info i have dug up is this:

5D6A Introduction Date:
The 5D6A was introduced in March 1955 with number 0100 and continued up through the 5E6

Bassman 5D6, 5D6-A (tweed)
0600 to 0900 - 1954

[eleventeen]

51K is an odd number.

Not really, plexi, 51K is a normal value in 5% resistor land, just like 10K, 15K, 18K, 22K, 27K, 33K, 39K, 47K, 56K, etc are the normal values in 10% resistor-land.

[tubeswell]

PI seems odd...

Both resistors are color banded 51K. No color fade on this end. One reads 54K & 55K
There in circuit so that sometimes makes readings off a hair. 51K is an odd number. Maybe they are or were 56K and mis printed.
Even so the resistor would drift up in value instead of lower in value i think

Maybe they both measured about 50k at the time of installation?

[HotBluePlates]

The changed font for the "47k" in the schematic posted above suggests it was a later addition to the schematic.

That font looks familiar, probably from Dave Funk's Tube Amp Workbook (my copy is in another state).

50k was probably the typical value at the time, with 47kΩ being the later edited value when the schematic copy was printed (probably in a book).

Maybe they were out of 50kΩ (or 47kΩ if that was truly the correct value) that day, and used 51kΩ to get the amp built. Each of those has the gold 5% tolerance band, and I can't remember ever seeing a resistor in a vintage fender amp of tighter tolerance than 10%. So I think that value was unique to this amp (or others made that day/week), and swapped to get 'r done.

[drgonzonm]

I was going through the layout on the posted website.  I noticed that a ground and a 220K resistor were not shown in the pictures.  On the 5D6a layout, this would appear between the 10 meg resistor, and a node branching to a cap and another 220K resistor found in the tone stack.

I am not sure how much the chassis was stripped, because I couldn't find in any of the pictures the 1 meg resistors shown at the jacks.  (Builder beware!!!)  

Regarding the selenium diode.  Replace with a silicon diode.  Failure of the diode to heat, results in poisonous gases being produced.  

This is shot of the updated 5D6b circuit board.  http://bb.steelguitarforum.com/viewtopic.php?t=167347&postdays=0&postorder=asc&start=0.  It does not show the 220K resistor as discussed above.  

Also, the 5D6 seems to have pin 9 grounded to the chassis.  (Easy upgrade)

[plexi50]

Interesting thread. Do i need to store my amp in a walk in safe? I can wait to finish the 5E3 cab so i can start working on the 1954 5D6A

[HotBluePlates]

I was going through the layout on the posted website.  I noticed that a ground and a 220K resistor were not shown in the pictures.  On the 5D6a layout, this would appear between the 10 meg resistor, and a node branching to a cap and another 220K resistor found in the tone stack.

That is the horizontal 220k in picture 5, reply #18 of this thread.

I am not sure how much the chassis was stripped, because I couldn't find in any of the pictures the 1 meg resistors shown at the jacks.  (Builder beware!!!)

They are mounted directly on the jacks in Fender amps, and we don't have any closeup photo of the input jacks in the inside of the amp. I'll bet you $100 they are there.

Regarding the selenium diode.  Replace with a silicon diode.

Probably a good idea, but the selenium rectifier drops some voltage, at least more than a silicon diode. As a result, you may have to tinker the resistors in the bias circuit to land back on your desired bias voltage.

Also, the 5D6 seems to have pin 9 grounded to the chassis.

The few close-up shots of a tube socket in this thread show 2 filament wires, and pin 9 of preamp tubes not grounded. The overall shot also shows 2 wires for the pilot light.

However, the one-wire filament circuit was dead-nuts common in mid-50's Fenders. They generally grounded one filament pin of each tube to the chassis near the socket, grounded one of the pilot light terminals to its mounting bracket and grounded one side of the filament winding at the PT along with the high voltage center-tap.

But if this amp does have a filament center-tap as indicated in the schematic, then they would have used a two-wire filament circuit.

[HotBluePlates]

Interesting thread. Do i need to store my amp in a walk in safe?

That guy seems to be hyping things a bit, maybe to make his hand-built amps look like a bargain by comparison.

There was a guitar shop in Nashville that had an all original 5F6A Bassman in quite excellent condition that had been owned by Luther Perkins (guitarist for Johnny Cash), along with a signed letter from Perkins that confirmed the serial number and the he indeed owned and used the amp. I think they wanted $4k (maybe slightly less), and that was with the provenance linking the amp to a famous player.

[Platefire]

Un-Real!!!! Well all I say is both these vintage amps fell in good hands to become even better than they were in their original state. I will be looking forward to following their restoration progress. BTW-have you established their approximate year of manufacture??
Platefire

[plexi50]

The pots are dated 1954. Selenium rectifier dated 1954. The OT i dont know what the date code TRIAD 2485 means yet. Pics of 1 megs,220k.

[Platefire]

Wow! That when I started the 1st grade. 

[plexi50]

CT's Grounded. Preamp and power tube filament wiring

I am in the first grade, Starting all over again. This is the proof! 

[sluckey]

The selenium rectifier in that very low current bias circuit is likely to never be warmer than room temperature. It's already lasted +50 years and will likely be still working after another 50 years. That one is tiny enough that it's not much of a threat, especially in that circuit. I would leave it be if the bias voltage is what you expect. Like HBP said, you'll have to mod the bias circuit if you replace it with a silicon diode.

[plexi50]

Im keeping all that i can stock. I have not gotten around to checking all the resistor values. Maybe i will do that later today to get that out of the way. Not certain yet on the health of the coupling caps. I have some yellow Jupiter Astron style caps im going to put in the 5E3. Im ordering the Jupiter Astron style red caps for this amp. Those Astrons are known leakers and after 59 years im sure they wont mind. Nothing lasts forever/

[drgonzonm]

FYI,

I was comparing a 5d6, with serial number 0035 to the 5d6a which is the topic of this thread.  A comparison of layouts between the 5e6 and the 5d6a has been discussed.   As I have discussed there are some minor differences between
5d6a and 5e6s.  Maybe this is not the thread to discuss the 5d6, as I may be confusing this threads discussion. 

Basically, I just saying, I believe there are some major differences between the 5d6 and 5d6a, where I am suggesting two links to review what work has been done on a 5d6 with a stamped serial number of 0035. 

Regarding my ability to find missing 1 meg resistors, I won't take that bet,  because, I expect them to be there.   The clarity of the photographs, I have downloaded is not that good. I am going pixel blind from zooming. 

Regarding pin 9 (12a_7's) on chassis 0035 being grounded to the chassis; from the solder traces shown, other pictures from the steelguitar forum, and a review of Fender D schematics, I feel comfortable that chassis 0035 was assembled with the pin 9 grounded.

Given that the Bassman was being upgraded to support Leo's new bass guitar, Improvements  on the 5d6a seem reasonable.

To avoid other confusion, I start a new thread on a comparison of a possible 5d6 circuit and the 5d6a circuit. 

This thread, has provided me some information, I had speculated about, and shot down other speculations. 

Thanks guys.     

[plexi50]

Cleaned the tube panel side down and sockets. Final clean of transformers. Light steel wool and WD on iron laminates. Dam that front panel looks like it was just made  

[eleventeen]

Very, very nice. Thanks for the pix, too!

[plexi50]

Talk about manic! I have this NASCAR wax cleaner called fastwax. Comes in spray cans. Killer stuff.

[Willabe]

Final clean of transformers. Light steel wool and WD on iron laminates.

Isn't WD-40 is conductive? Or was it just that it displaces moisture?    

Iron looks great now for it's age.

Interesting to note that the PT has a copper band around it that far back in Fenders line.


                Brad      

[plexi50]

Final clean of transformers. Light steel wool and WD on iron laminates.

Isn't WD-40 is conductive? Or was it just that it displaces moisture?    

Iron looks great now for it's age.

Interesting to note that the PT has a copper band around it that far back in Fenders line.


                Brad      

I just lightly wiped WD on with a rag. I didt spray on the transformers them selves. Definatley going to be great when the cab,speaker and chassis are completed

[PRR]

> Isn't WD-40 is conductive?

Zilch for all practical purposes.

One of the few good uses for WD-40 is *temporary* drying/sealing damp ignition wires. It does tend to displace water, and does NOT bleed-off the spark.

It's kerosene. Very selected fraction of all the stuff sold as kerosene, but just petroleum distillate.

[plexi50]

I have been looking at several 5D6 bassman pics and found a 47M  & 100K resistor coming off the 270K voltage dividers in the pic below. The 5D6A has a 10M & 220K combination. Cant verify the 5D6 feedback resistor yet. Im thinking it is 20K as is the 5D6A. It's in hiding just under the last PS cap pic. Still looking for differenced between the 5D6 & 5D6A

[sluckey]

found a 47M & 100K resistor

That's really a 4.7M. A 47M would be yellow/violet/blue.

Still looking for differenced between the 5D6 & 5D6A

Why? Didn't you say your amp is a 5D6A?

[plexi50]

found a 47M & 100K resistor

That's really a 4.7M. A 47M would be yellow/violet/blue.

Still looking for differenced between the 5D6 & 5D6A

Why? Didn't you say your amp is a 5D6A?

I misinterpeted the last band (green)
Yes my amp is the 5D6A. Maybe i should have started another thread on 5D6. Just curious what the differenced are between the cicuit boards