Gretsch 6159 Dual Bass 1966-67 Era (Unusual Configuration)

[Jim Nasium]

Hello All,

I am new to the forum and tube amps, in general.

A friend of mine graciously bestowed to me a Gretsch 6159 Dual Bass amp that I want to get back to original configuration, and working again. I intend to keep this amp and use it for live music application, but may record some with it. So, I am going to change out some parts with like spec parts, and will be attempting to assemble a cross reference parts list for new manufactured replacement spare parts to keep it alive as long as I am.

I will also need to perform a three prong conversion.

This thread is to chronicle my journey of gaining insight on this amp, and to hopefully help others that may be seeking good pictures and a restoration parts list, for what appears to be a not well documented amp aside from a few threads on this forum.

Below are some pictures. You'll see that this particular amp has one speaker facing front, and the other is facing back. The date codes for both Jensons are in mid 1966, and other parts date in that era as well, so I believe it is a 1966 year model, but I suppose it could be a 1967. I have found no pictures on the internet or in any catalogue of this configuration.

[Jim Nasium]

Schematic:
https://el34world.com/charts/Schematics/files/Gretsch/Supro_gretch6159.gif

Observations:
The On-Off-Standby switch has been replaced with a On-Off switch.

The Bass channel tone pot has been replaced and it appears that the capacitor between the volume and tone pots was omitted when this was done. Both bass jacks worked, however the pots were very scratchy when  turned, and there was a lot of hiss.

The Tremelo channel did not function with either the Guitar or Accordion jacks.

Three jacks had been replaced with the enclosed plastic type. The metal cover plates that I have seen in some of the pictures of the front faceplate style 6159, were not installed inside, so i am curious as to what their intended function was.

[Jim Nasium]

My plan is to replace all the potentiometers, the power switch, and the jacks to just baseline those items and get them working uniformly, as a start, including whatever missing capacitors are needed. From there the trouble shooting will begin.

So, my first question is around the potentiometers. The schematic specifies all the pots as 500k. The OEM pots are CTS. I will replace the pots with CTS 500k 450G (splined brass shafts, instead of the nylon shafts). There are six pots: Bass - Volume & Tone, Tremelo - Volume & Tone, Tremelo - Speed & Intensity.

Does anyone know, with certainty, what pots were linear vs audio taper originally?

My second question is centered around the On-Off-Standby switch. I have purchase a DPDT Carling switch.  I have seen pictures of multiple jumpers on that switch, and a wire soldered at the top left post, but the schematic does not show this. 

Does anyone have a more detailed sketch of how that switch should be wired?

[j_bruce]

Jim,

I repaired one of these during the covid lockdown. The one I worked on was just the chassis and such and it had a lot of rodent damage. Once done it is a really nice sounding amp so I feel it is well worth your while to get this one back working.

I swapped out all the electrolytic caps, new PT, all new pots on the front panel. I used all audio taper and it seems to work as expected. I had a hard time finding a pilot light that fit the hole and looked somewhat original so I improvised with an LED and adjusted the circuit to work.

Good luck with your project,
Jerry

[sluckey]

Nice project. We like BIG pics, especially when asking specific questions, or just wanting to show details.

Before you replace any pots buy a can of De-Oxit electronics cleaner and apply to the pots and jacks. Exercise the pots by turning end to end several times while wet. This will most likely cure the scratchy pots issue.

That schematic from Hoffman's library has some errors. There cannot be a grounded center tap on the high voltage winding, or you cannot use a FWB rectifier as shown. One or the other is an error. Have to look at the amp to be sure which is right.

Also, the power/standby switch is not drawn properly. You need a DPDT ON-OFF-ON switch and it needs to be wired like the attached corrected schematic. AES has the correct switch...

     https://www.tubesandmore.com/products/switch-carling-toggle-dpdt-3-position

Good luck.

[Jim Nasium]

Thank you both for your responses.

j_bruce - please check email and/ or PM. I have viewed and reviewed your thread many times for reference. If you are okay with it, I'd like to pick your brain on a few things I have questions about, and you have firsthand experience with.

sluckey - thank you for the the corrected drawing. That answers  a lot of questions I had about the switch. I have ordered the Carling DPDT switch with the solder lugs. I have looked at this drawing many times and never found the "C" at the top of the schematic. Ha! Correct me if I am wrong, but it appears the drawing would get me back to spec for a two prong power cord; is that correct? If so is there a schematic for a three prong conversion?

[sluckey]

If so is there a schematic for a three prong conversion?

Don't need one. Just connect the green wire to chassis. Black wire to the switch. White wire to the PT.

[j_bruce]

Jim,

I have been sick the last few days, I saw your note and will be in touch in a day or two once i am feeling better. I am not sure how much I can help but I am happy to try.

The "point c" eluded me a for a bit as well.

[Latole]

". Before you replace any pots buy a can of De-Oxit electronics cleaner and apply to the pots and jacks. Exercise the pots by turning end to end several times while wet. This will most likely cure the scratchy pots issue."

-Sluckey

____________

Follow this advice. With the right contact cleaner you will save the pots.
Don't forget, if a signal cap is leaky you may hear scratch on pot, replace leakey cap

Another post in 2020 ; same amp :  https://el34world.com/Forum/index.php?topic=25897.0

[PRR]

...The "point c" eluded me a for a bit as well. ..

Point "A" eluded me. Found it. You might put this cheat-sheet in your folder. (I assume there is no point "B"?)

[Jim Nasium]

Thank you for the great schematic help.

I've been a bit inundated with some things that took me off of this project lately.

I have a few questions.

1. Is there a particular recommendation for replacement wire? At least one of the wires has been cut short from the hack that installed the single throw replacement switch, and did not connect the "C" wire in the schematic. I am putting the proper DPDT switch back in and will need to replace that wire.

2. Regarding capacitors and resisters. Are there particular capacitors and resistors that are the most highly regarded for amplifier applications? I know this is a broad question, but any help will be appreciated. The capacitor that should be in the location between the tone and volume pots for the bass channel, is missing. See low quality picture scrounged from the internet.

3. Lastly, any recommendation for three prong cord specs would be appreciated.

[Jim Nasium]

Also, what Switchcraft jack be a good replacement jack for the Tremelo footswitch jack?

I am not certain this is correct in my amplifier as well. It appears the jack should be ungrounded, so I would need some type of insulated mounting hardware.

[PRR]

> the jack should be ungrounded

https://hoffmanamps.com/MyStore/catalog/parts8.htm
4 Solder lug Marshall style jack
Chrome or black bezel. Note the note about needing a washer.

If you have a pending order at a pedal-parts shop, these are VERY common in that use. Or you could butcher an old disappointing pedal.

[sluckey]

Also, what Switchcraft jack be a good replacement jack for the Tremelo footswitch jack?

Links to Hoffman's parts...

     Switchcraft L12A jack

     Shoulder Washer

[thetragichero]

maybe purely cosmetic but if this were my project while components were removed i'd take a wire brush followed by a tooth brush with chrome polish to the corrosion inside the chassis

[j_bruce]

Also, what Switchcraft jack be a good replacement jack for the Tremelo footswitch jack?

Links to Hoffman's parts...

     Switchcraft L12A jack

     Shoulder Washer

That's what I did , at Sluckey's suggestion.

Worked great, not noticable from the front.

[Jim Nasium]

Nice project. We like BIG pics, especially when asking specific questions, or just wanting to show details.

Before you replace any pots buy a can of De-Oxit electronics cleaner and apply to the pots and jacks. Exercise the pots by turning end to end several times while wet. This will most likely cure the scratchy pots issue.

That schematic from Hoffman's library has some errors. There cannot be a grounded center tap on the high voltage winding, or you cannot use a FWB rectifier as shown. One or the other is an error. Have to look at the amp to be sure which is right.

Also, the power/standby switch is not drawn properly. You need a DPDT ON-OFF-ON switch and it needs to be wired like the attached corrected schematic. AES has the correct switch...

     https://www.tubesandmore.com/products/switch-carling-toggle-dpdt-3-position

Good luck.

I have been attempting to sort through the power switch. I bought the correct switch. The existing wiring is shown in the photos, and described below. I made a sketch and attached it also, attempting to reconcile between existing wiring, and the schematic to try to make some sense out of it.

In the amp, as is, the top right switch lug, a black lead goes to the light, and then is orange to the fuse ring, then on to the PT wire.
From the fuse ring, the .01 cap is going to ground.
Also, from the top right switch lug, there is a blue wire going to the other PT lead.
One AC power cord wires goes to the middle right lug.
The other AC power cord wire goes to the rear lug of the fuse.
As is, the Brown V5 wire was loose in the enclosure (not attached)
No ground was directly connected to the switch.
It appears that I should jumper the right top and bottom lugs.

If someone more experienced than I am could give me feedback on the proposed sketch, I would appreciate it.

[sluckey]

I would wire it like the attached pic. Totally remove and discard that disc cap. And don't actually use a wire nut for the splice (just drawn that way for clarity). Instead, use an empty lug on a terminal strip. I see several in your pics.

[Jim Nasium]

sluckey,

Thank you very much for taking the time to draw that sketch. By the end of this project I want to have sketches that will help the next person that runs across one of these amps, in my situation, so I am taking the time to make sketches with that in mind.

I am curious to know the thinking behind removing the capacitor. Would you kindly explain that? I have read elsewhere that it eliminates a potential source of hum, and I have also read that it is not needed. Certainly you have real world experience both ways that would educate me.

I really like the idea of using a lug on a terminal strip instead of wiring everything to the fuse holder. I was going to change out the fuse holder anyway, because it is loose and will not tighten up securely on the plastic threads. To me it makes sense to have as little wiring on components as possible to ease future maintenance.

[sluckey]

Back in the good ole days before three prong power cords, it was possible to get a "sting" or even a nasty bite while touching your guitar strings and also touching your buddy's strings or amp chassis. Even worse if your lips touch the mic! It was all because of that cap. Back then the fix was to flip a "ground" switch or reverse the power cord plug until no one got shocked. Something you had to do every time you set up to play.

That cap became known as the death cap. Google it. Lot's of good info but also a lot of mis-information too.

Then along came the three prong power cord. Now every amp had it's chassis hard wired to earth ground via the green wire connected to the chassis. No more nasty shocks ***IF*** the house wiring is correct. But what if the house wiring is not up-to-date with grounded outlets or just plain wired wrong? It happens. And you can still get a nasty shock. So, common practice became just remove the cap.

However, the cap does serve as a line filter and can reduce hum and/or line noise. Now we have a special cap to be used as a line filter. It's called a Class Y cap and two caps are connected from line and neutral to chassis ground. These caps are made in such a way that they will never fail shorted. Failures are always open circuits and can not harm the musicians.

So, if you want the benefits of that cap, replace it with a Class Y cap. Better yet, get two Class Y caps.

[Jim Nasium]

I had some things come up that took me off this project for a while. Back on it.

Remember, this is my first amp work.

I replaced the diodes that construct the rectifier.

Now, I am replacing the old can cap. The original can cap was 20/10/10. The new one is 20/20/10/10. I know others would have just built a cap bank. I chose not to.

What I have encountered is an extra 20MFD cap that I do not see on the print. I have a reference picture that I found from someone else on the internet, and I see the exact same thing I have, physically present. I am a bit stumped.

The situation is that coming off the 20MFD cap in the can cap (picture with green arrow), is directly soldered another 20MFD cap, then on to ground. Also there is a closeup picture of this.

The print does show a separate 20 MFD cap, and there is a separate 20 MFD cap (green circle, no arrow) that goes to the power valves.

Print attached.

So, is it possible that both can caps had bad, 20 MFD sections, and these are replacements? Is it possible the print is wrong? Am I missing something on the print?

If this separate cap coming off the can cap is supposed to be there, on the new can cap, can I jumper over to the extra 20 MFD cap in the can, instead of having the separate cap hanging off?

Thanks for any help.

[sluckey]

The original can cap was 20/10/10. The new one is 20/20/10/10.

Are both cans the same size?

So, is it possible that both can caps had bad, 20 MFD sections, and these are replacements? Is it possible the print is wrong? Am I missing something on the print?

I don't think so. I have examined all the pics of your amp and based on the quality of the solder joints I believe those two extra axial caps were installed at the factory.

If this separate cap coming off the can cap is supposed to be there, on the new can cap, can I jumper over to the extra 20 MFD cap in the can, instead of having the separate cap hanging off?

Yes and remove the cap that's connected directly to the can. Then just jumper the two 20µF sections together. The other 20µF axial cap that's connected to the 1K/7W resistor and two green/white wires should be replaced.

I've attached a revised schematic that shows the missing cap and should clarify how all those caps are connected.

[Jim Nasium]

Thank you sluckey!

The can caps are different in physical size. The new one is a larger diameter. I will file the hole larger and make it square, and drill new mount holes.

I will jumper the two 20 MFD can sections, run one can cap ground lug to the board ground, and replace the other 20 MFD cap, this weekend. I am also replacing all the other electrolytic caps. 

Thank you very much for the updated print.

[sluckey]

The can caps are different in physical size. The new one is a larger diameter. I will file the hole larger and make it square, and drill new mount holes.

This will probably make mounting that new can much easier and neater...

     https://www.tubesandmore.com/products/mounting-plate-metal-1375-can-capacitor

[Jim Nasium]

What's the lowdown on ceramic disc caps?

While I am waiting on my can cap mounting plate, I am working on replacing the pots I had already bought.

On the guitar/ accordion channel, there are a couple of ceramic disc caps. If you scroll up you can see them in one of the pictures. This is the channel that was not working at all, when I received the amp.

One spans across the tone pot to the volume pot ground lug, which has a wire going to ground. It has written on it RMC .0033 20% Z5U.
 
The other cap spans across the other two lugs on the volume pot. It has written on it RMC 500 Z5U 20%.

I am finding it difficult to select capacitors, based only on that information, because there is no kv information?

Would most people use a different type of capacitor, or stick with the ceramic? Any advice on the kv to select?
Is Y5P a better selection than the Z5U? Is any one brand preferred over another for this application?

[PRR]

What's the lowdown on ceramic disc caps?

That's a very open-ended question. Let's not go there.

Any advice on the kv to select?

The highest voltage in the whole amp is 400VDC. The final stage plates will kick higher but there's no caps there. A 400V rating should be ample.

Actually, tone-caps see a few volts normally and up to a few hundred volts when severely beaten (drunken 13 year olds in a garage when the adults are out). So 250V may last a long time.

Ceramics in this size "may" have a sound. What do you want? Preserve the original tone (if possible)? Or do it "right" (these caps were ceramic for price)?

Why do you think these caps are bad?

[sluckey]

Lots of older stuff used ceramics probably because of price. I would not replace them just because they are ceramic.

This was a high quality Roberts tape recorder deck before I butchered it. I harvested the transformers and all the ceramics that had 1/2" leads.
http://sluckeyamps.com/smoky/rr3.jpg

This is a Hammond AO-63 organ amp that I converted to a guitar amp. Ten ceramics caps. Some original, some added by me.
http://sluckeyamps.com/hammond_2/big_guts.jpg

I used three ceramics in my Lil Smoky toaster oven amp just to be a little different.
http://sluckeyamps.com/smoky/4.jpg

[Jim Nasium]

Well, I went ahead and left the original ceramic disks in place.

I finalized all the other work I had planned, and re-soldered the speaker wires, then plugged in the cord, flipped the switch to standby, pilot light came on for a second, then went out. Poof...blew the 3 amp fuse.

I tried the same for all the channels, and same result.

I have a question. There are two black wires coming from the PT. I might have gotten them swapped around. Would this matter?  They can be seen as they were originally in the picture below. One is soldered to the fuse, and the other is soldered to a blue wire going to the switch.

[sluckey]

Disconnect the two PT red leads from the diodes. Still blow?

[Jim Nasium]

Disconnect the two PT red leads from the diodes. Still blow?

Finally got back to this. With the two red PT leads disconnected, the fuse does not blow.

[Jim Nasium]

Hi sluckey,

Do you have any thoughts on the the fuse not blowing after disconnecting the red leads coming from the PT?

[sluckey]

Bad diodes or shorted filter cap(s). You'll have to disconnect one lead of each diode in order to check it. Use ohm meter to check resistance of each filter cap to ground.

[Jim Nasium]

Update:
I had to again put this down a while. I unfortunately reached a bit of my limitation on checking out components. I can follow instructions pretty well, but still have much to learn diagnosing things since this whole world is new to me.

 I found an aspiring amp builder in the area who was willing to work with me, not just for me, and he has been a tremendous help.

As Sluckey guessed, it was a capacitor. Turns out my brand new $40 can cap was bad, and grounding out a lot of things. When I soldered it in, I did heat sink with a pair of hemostats. Maybe I burned it up. Who knows? The old one is in and no more fuses blowing. Yeah!!! Bass and Guitar/ Acc channels sound truly amazing.

Now we have another problem. The tremelo is not working. We have been studying these circuits pretty hard, and watched Uncle Doug's video on the subject as well.

The thought was perhaps the phase was cancelling out due to a bad cap. So from V3 -6 we replaced all three of the tremelo caps that should get the wave form back in phase. That did not work.

We then replaced all the tubes, which was going to be done anyway. Did not work.

Now we are looking at the switchjack for the footswitch. I replaced the jack that was in it, which was plastic, with a Switchcraft 12A and the jack is insulated from the faceplate because it is not grounded.

As it stands right now the shunt lug is not wired to anything. As I look at this more closely, I believe the shunt should be jumpered to the sleeve (ground). Thoughts?

The tremelo should work without a footswitch in it.

[sluckey]

The shunt must be connected to the sleeve just like the schematic shows.
That 12A jack must be insulated from the chassis. The correct way to do this is to use two shoulder washers. Like this...

[Jim Nasium]

YEAH!!!!

The whole thing is working, all channels, and the tremelo!

I have collected a ton of reference documents, including a complete original and cross referenced spare parts list. The only thing I do not have a verified spare for is the output transformer and power transformer. I am about 1/3 finished with an as built layout of the components.

I'll get some pictures posted of the final component wiring, as well, for the next person. Should be finished up in a couple of weeks.

[PRR]

Why didn't they do it this way? (Assuming the foot-switch has no on/off marks.)

[sluckey]

Good ole Valco engineering. My Supro is the same way.

[bmccowan]

The only thing I do not have a verified spare for is the output transformer and power transformer.

I used to buy Valco spec transformers from Magnetic Components/ClassicTone. But they closed down and not much stock is out there. A good place to look, besides Hammond, is Musical Power Supplies https://www.musicalpowersupplies.com/  I have found the quality and selection to be good. General rule of thumb is that Valco tended to cut it close on specs/sizing - if anything the trannies are a bit undersized. Some say this adds to their unique sound. I suppose so, but there are a lot of factors that likely add up. Biggest contributors in my opinion are the paraphase phase inverter and the use of fairly small filter caps combined with some additional small filtering caps at various points.
Congrats on getting her done - I recently rewired an earlier version of that amp: tube rectified with a split chassis, 2x12 facing the same direction, but otherwise the same schematic. Too loud for my purposes but great clean and OD sounds.