Gretsch 6159 "Dual Bass" Update: It's finished!

[j_bruce]

So I am waiting on a pot for my Airline project and decided to get acquainted with my next project a Gretsch 6159 Dual Bass. This belongs to a friend who is a great singer/songwriter that I have performed with a time or two and written a song with. (If anyone cares I will point you toward it on pandora.)

She is a great bass player and wants to put this amp to use if I can make it run for her. It seems to be pretty original save a 20 uf@450v filter cap tied to the can cap incorrectly and a botch job on the power switch, plus a three wire power cord addition.

https://drive.google.com/open?id=1SyEnhY1GZjp9TKS0F2rBLeHSZxEAp7OB

https://drive.google.com/open?id=1QESXa80-0FsOm5QQNUiSpS1uWa9ErYx1

The power switch barely fits where it belongs so I am going to replace entirely with a new switch and suitable wire.

https://drive.google.com/open?id=1oiGmthw5YNZv06W7--b3HHPkfnf_OsQn

You might also notice that I am using two terminal strips to build a new "can cap substitute" since the replacement cost $40 versus $1.50 for the terminal strips and using the caps the owner gave me.

I am planning on replacing all those paper wrapped .05 uf caps, but what about the rest? I am inclined to wait and see how it works before I go crazy on all the caps. the paper ones I understand are prone to failure and she gave me a bag of suitable replacements so I will swap them.

The tremolo switch jack was broken also so it's getting a new jack. The one you can see is not a switching jack so it will go into my spare parts bin.

I will need to find a pilot light.

The schematic can be found right here thanks to our host:
https://el34world.com/charts/Schematics/files/Gretsch/Supro_gretch6159.gif

Cheers!
Jerry

[Latole]

Nice project.
I'll leave paper caps in, unless you can test them with a meter or capacitor checker and they test out of value.
I'll replace all those white 'lytic bypass caps too.

You filter caps replacement is a good idea. multi-can are very ( too ) expensive.

[j_bruce]

So I got started in this thing and replaced the power supply diodes due to one being bad and replaced the cap can with a bank of caps and got all the stray repairs resolved.

Then I tried to power up using a dim bulb. Not good: full on bright.

Did some nosing around and found that the primary to secondary on the PT has 3.6 ohms resistance with both the primary and secondaries disconnected from the circuit. So unless someone corrects me here, I think I better go shopping.

Cheers
Jerry

[sluckey]

You need to carefully examine the PT and diodes connection in the amp. The schematic has an error that will kill a PT and diodes if connected as per the schematic. The schematic shows a FWB with the negative pole of the bridge connected to ground. But the schematic also shows a CT that is also connected to ground. It cannot be both ways.

One of your photos looks like the amp is probably wired for a FWB but I can't be sure because I cant see all the diode leads. (Anode lead on the leftmost diode is hidden).

You must resolve this before you purchase a replacement PT. If your actual amp is using a FWB then that Classic Tone PT will not work!

[j_bruce]

Sluckey,

Thanks for taking a careful look and noticing that on the schematic. The diodes are wired as a FWB, the current transformer has two black primary leads, two red HT leads and two green heater leads plus a green/yellow CT lead that is grounded. I suspect that the CT concern you have is aimed more towards the HT having a a CT.

So I would say the error is the CT shown on the schematic as there is not one in the amp.

Again thanks for looking closely, and giving me another lesson!

[sluckey]

I thought it was most likely a FWB in your amp and just a drawing error on the schematic. But, this means you cannot use the Classic Tone 40-18060 PT in your other thread.

[DummyLoad]

have a look at the hammond 276X. rewire diodes for full wave CT grounded. they should be replaced anyway. PSUD2 points to that part getting you very close to the 400V B+ stated in schematic. from schematic, power output stage is drawing ~150mA at idle and rest is about ~5.2mA.

have you checked with mercury magnetics - they may have one on the shelf for SS mode dual bass - there was a tube rectifier older model that used a 5U4 - be sure that they aware of that.

replace the can with T&T or JJ 32uF/32uF 500V 1-3/8" can cap and tack a 10uF-220uF 450V inside - looks like there's room for that.

be sure to test the OT - catastrophic PS failure may have killed that part as well.

--pete

[DummyLoad]

http://www.classictone.net/40-18103.html

http://www.classictone.net/40-18103.pdf

that part may work for you as well - B+ may be a bit lower but allows you to keep full-wave bridge rectifier. 39V secondary NOT used - tape off the wires individually.


--pete


EDIT: should have read your other topic - how to choose... apologies, this is same part you picked.

[j_bruce]

I got the PT installed and made my way through powering up without too much challenge.

Had a bad 120 hz buzz and a bit of background noise coming with the volume. I swapped the volume pot and tone pot and got that noise down to very little. The tremolo pots are dicey at best but I do not think that is the heart of the issue. I will probably just swap all the pots in the end.

But the buzz just keeps going. So: pulled the 4 12ax7s and it is quiet as can be, put in v4 and the buzz is right back. tried a different 12ax7 and same buzz. with only v4 the volume knob effects the buzz but only by 10%+-.

So i tested everything connected to the PI (v4) and cannot find any bad joints or out of spec components. Then I put all the tubes back in and measured voltages to be:

Power tubes: plate 410v on both, cathode 31.6v on both, pin 4 (screens?) 403v

V4, PI: pin 1 172v schem is 100! pin 6 206v schem is 90! Yikes these worry me, but the 270k resistors are on spec. the cathodes match te schem at 1.5v and 1.98v

V1 plate is at 195v schem is 180v, cathode 1.63v schem is 1.7v

V2 Plate 1 is 286v (270v schem), plate 2 is 202v (schem is 105)! cathodes are on spec at 2.9v (2.8v) and 1.68v (1.6v)

V3 Plate 1 would not give a stable reading, plate 2 is 354v with no schem number, cathodes are at .6v (.7v) and 2.9v (2.8)

The schematic is here: https://el34world.com/charts/Schematics/files/Gretsch/Supro_gretch6159.gif

it is original except what I have done and the PT was swapped so it no longer has a center tap on the Ht, just the FWB.

[shooter]

V4

what's the vdc at pins 2 & 3

EDIT, found you called 'em out

[shooter]

the cathodes match

thinking out loud;

the cathodes "set the tone"  Vk/Rk = tube current, so that's "normal"

[DummyLoad]

did you add a pair of 100R 1/2W resistors to the filament winding for a virtual center tap?

the classictone replacement PT you bought does not have a center tap on the filament winding.

the virtual CT created by the 2 x 100R resistors can be tied to ground, or if you prefer, tie the virtual CT to pin 8 of either 6L6.

see attached.

[j_bruce]

did you add a pair of 100R 1/2W resistors to the filament winding for a virtual center tap?

the classictone replacement PT you bought does not have a center tap on the filament winding.

the virtual CT created by the 2 x 100R resistors can be tied to ground, or if you prefer, tie the virtual CT to pin 8 of either 6L6.

see attached.

I did not do that, I can tackle it but I will have to find a couple of resistors. being new to this I don't have a supply of parts on hand. I will check in the lab at my day job tomorrow, a couple of 100 om resistors should not be hard to find there.

Thanks for catching that!
Jerry

[PRR]

> a couple of 100 om resistors

Exact value not critical. 33r may run hot, 1k may give poor action; either is a lot better than no ground reference.

They should be similar to better than 10%.

[j_bruce]

virtual center tap did it it is quiet as can be now!

The tremolo channel has a lot of scratchy noise in the pots so I am going to change those out and this thing should be ready to rock!

I will check those voltages again just to be sure all is well.

Thanks guys,
Jerry

[j_bruce]

Thanks to plenty of great suggestions and a lot of reading I have this thing mostly working now.

The regular channel is sounding good with nice tone and good volume. But the tremolo is a bit noisier at high volume settings and it does not seem to have a wide range of intensity and only one speed. When set on full intensity I definitely get a pleasing tremolo effect but not the big oscillating tremolo of my Kalamazoo Model Two. I ran across an Uncle Doug youtube vid of how tremolo works so I will have to view that again and see if I can gain some insight. The way it is is very pleasing to my ear but not how I thought it should work.

I could return it to the owner with my head held high as it is very playable, but I would like the tremolo to work a little better and have a bit less hiss. Any thoughts appreciated.

I also learned one interesting repair tip that I will share with you: Cheap LED magnifying lights cause a pretty strong 60 hz hum when positioned close to V1. Your welcome. 

Cheers
Jerry

[sluckey]

and only one speed.

Schematic shows a 500K speed pot. Replace with a 3M-RA pot and you should have a nice range of speed.

[j_bruce]

Schematic shows a 500K speed pot. Replace with a 3M-RA pot and you should have a nice range of speed.

RA = Reverse Audio taper?

happy to give that a try, thanks!

[j_bruce]

I have been trying to puzzle out and find the problem in this tremolo but I just cannot find the culprit.

Here is what I have done:

carefully rechecked the circuit several times to verify that it is wired per the schematic. It is

Checked each component to verify values. All in spec or replaced.

Borrowed an oscilloscope and when I probe the cathode of V2a I can see the oscillation at about +/-.02 volts. The speed is actually working which is easy to see on the scope. But the intensity never changes when I turn the knob.

So the weak tremolo is weak intensity, the speed works ok but the intensity is so low that I can't really hear it with the speed up.

The schematic is here: https://el34world.com/charts/Schematics/files/Gretsch/Supro_gretch6159.gif

I am stuck, it's a pretty nice amp other than the tremolo.

[shooter]

when I probe

looking at the schematic link you posted earlier;
the footswitch works?
what do you get on the plate?, scope or meter VAC

[j_bruce]

when I probe

looking at the schematic link you posted earlier;
the footswitch works?
what do you get on the plate?, scope or meter VAC

no foot switch; the tremolo is on with no foot switch plugged in isn't it? Sure looks that way to me. 

The plate of V3a is at 341v on my meter.

So something that just occurred to me is if the tremolo jack should be isolated from the chassis? It is not shown as being grounded itself. I have it grounded via the jack to chassis aspect of the shaft of the 1/4" plug.

I bet that is the problem, taking a break to go test! 

(Cue up Final Jeopardy soundtrack . . .)

 

 

YES! That fixed it. The tremolo works great with the jack pulled from the face plate.

How do I isolate that jack? my thought is to use one of those plastic "Marshall" jacks. Any other options?

thanks for the reply Shooter,
Jerry

[j_bruce]

I just noticed the funniest thing: the eye balls on that emoji I posted just above move right in time with the Final Jeopardy soundtrack.

 

[sluckey]

Hoffman sells these insulated shoulder washers. I used them on my Supro which also requires an insulated footswitch jack. Scroll down a bit on this page...

https://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=MiscHardware&ORDER_ID=!ORDERID!




You can see them in my Supro chassis here...

     http://sluckeyamps.com/supro/supro.htm

[PRR]

> if the tremolo jack should be isolated from the chassis? It is not shown as being grounded itself. ...... YES! That fixed it.

Obvious in retrospect.

[PRR]

This also means if you grab the trem plug you will get a low-Volt low-frequency shock; if your trem plug touches a grounded object or dirt the trem signal is shorted out.

There's other ways to do this, but I do not see any strong reason to change.

[j_bruce]

Hoffman sells these insulated shoulder washers. I used them on my Supro which also requires an insulated footswitch jack. Scroll down a bit on this page...




You can see them in my Supro chassis here...

     http://sluckeyamps.com/supro/supro.htm

Ordered! Along with a board and some parts for a TOS by Tubeinit which I think will make a really nice harp amp.

Thanks for your comments and help with this Steve.

[j_bruce]

> if the tremolo jack should be isolated from the chassis? It is not shown as being grounded itself. ...... YES! That fixed it.

Obvious in retrospect.

Yep!

I probably won't make that mistake again soon!

Cheers!

[shooter]

I probably won't make that mistake again soon!

you're only required to fess up once, after that it legal to say; "man this works great"   

[j_bruce]

Man this works great!

Seriously, it works great.

Last night I got together with the owner of the two amps I have been learning on to try them out. The original deal was do whatever I wanted to them and he would pay for the parts used if he wanted to keep either when and if they ever worked again. So he brings his daughter with her vintage Epiphone Crestwood electric and she played the heck out of this thing. The tremolo channel has a great tone and the tremolo has a sweet spot to me that give a rich sound without obvious tremolo, fabulous. When cranked up it has a great drive tone to it. I is also dead quiet even dimed out.

He plugged it into a Crate 12" cab that has a Clelestion placard on it and that speaker sounded great with this amp.

In the end he was delighted to get this back working great and sounding cool with about $175 in parts to pay for. His daughter just got a new recording set up for her music room I will try to get her to provide a couple demo clips.

OK, I am done bragging. If you see one of these for sale buy it, or tell me so I can buy it.

Now, back to work on my new project: TOS by Tubenit

[Jim Nasium]

j_bruce,

I have a few questions regarding the replacement parts you used on this project.

If you can recall, what specific parts did you use in the following applications? I am trying to create a modern spare parts cross reference list for a similar application.

1. Diodes
2. Polarized caps
3. Paper caps
4. Ceramic caps

[j_bruce]

The guy who brought me the amp to try to fix had bought it with a bag of spare parts. Much of which was not the right stuff, but the caps were all in the bag so I used what he gave me for the electrolytic caps in the circuit. I replaced all of the paper caps and the other electrolytics.

for the filter caps I choose to make a filter module out of two terminal strips and used F&T caps.  there is a suitable cap can available but cost $40.

I did not replace any of the other caps, they all worked to plan.

The diodes 1N5408

[ShaneCW]

j_bruce,

 I am trying to create a modern spare parts cross reference list for a similar application.

If you have someplace you will be posting progress with this list please share a link here if you don't mind. I have a 6159 under the bench I plan on getting to one day.
I was told it had a bad PT, also noticed it has an extra octal tube socket up top for what I am assuming is a rectifier and it also had SS rectification wired in the bottom. Haven't dug into it yet, probably won't get to it until fall or winter. Looks like it's gonna be a bit of a hair puller. Lol

[Jim Nasium]

j_bruce,

 I am trying to create a modern spare parts cross reference list for a similar application.

If you have someplace you will be posting progress with this list please share a link here if you don't mind. I have a 6159 under the bench I plan on getting to one day.
I was told it had a bad PT, also noticed it has an extra octal tube socket up top for what I am assuming is a rectifier and it also had SS rectification wired in the bottom. Haven't dug into it yet, probably won't get to it until fall or winter. Looks like it's gonna be a bit of a hair puller. Lol

I have had to step away from this for a couple of months. Getting ready to get back into it. Search for 6159 and you'll find my post there.

I have got what I believe to be a good print for it, including the three wire conversion, and have some good progress on a parts list.

Getting ready to work on t a little each week to replace the diodes, can cap, e. caps, power cable, fuse holder (was cracked), main switch (wrong one was in it), jacks (several wrong ones were in it), pots, and the other caps.