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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 7:10 am
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Retroverbial wrote:
stratele52 wrote:
Good caps like F & T or Sprague Atoms cost just few dollars more for a $700 ( and more ? ) Vintage Reverb


Ha!

Double that $700 is a more realistic value for an original 6G15.

Arjay



Oh Yeah ! I have one :D


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 9:27 am
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Funny thing, I am working on an old Gibson with a Gibbs tank and a grainy reverb. Its OK with just a little volume, but gets nasty with more volume.
I found that the little beads on the end of the spring rub the mount due to sagging suspension. When they touch, it turns distorted.
To check for any sagging problems, simply place the reverb unit in different positions.
When I turned this one upside down it got better. When I stood it on end, the noise went away.
I opened up the tank and put my finger on each spring to dampen them one at a time. One was very different sounding.
I haven't repaired it yet, but the spring that rubs moves around more easily than the others.
There is a small disc of foam inside the brass tube that is supposed to be close support for the bead. I am suspecting that the hole through the foam is worn.


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 9:35 am
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Reverb tank are buit to work better in one position.

In wrong positions the weight of springs displace the magnets.


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 9:56 am
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Everything you ever wanted to know about reverb tanks and associated data......

http://www.oberlin.edu/staff/thinders/r ... everb.html

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 10:41 am
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Retroverbial wrote:
Everything you ever wanted to know about reverb tanks and associated data......

http://www.oberlin.edu/staff/thinders/r ... everb.html

Arjay

"Laurens Hammond of Illinois popularized the use of artificial reverberation devices through his church organs in the 1940's and 1950's. The early (pre-B-3®) Hammond®organs were sold to churches on the principle that organ music is greatly enhanced by reverberation..."

And not just organ music, Reverend Hammond! :lol:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 10:53 am
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TimsAudio wrote:
...I found that the little beads on the end of the spring rub the mount due to sagging suspension. When they touch, it turns distorted.
To check for any sagging problems, simply place the reverb unit in different positions.
When I turned this one upside down it got better. When I stood it on end, the noise went away.
I opened up the tank and put my finger on each spring to dampen them one at a time. One was very different sounding.
I haven't repaired it yet, but the spring that rubs moves around more easily than the others.
There is a small disc of foam inside the brass tube that is supposed to be close support for the bead. I am suspecting that the hole through the foam is worn.

Really good info. I had read that some folks "fix" their reverb pans by putting some glue on the spring ends to stabilize the connection but that sounds kinda wonky to me. I will take a look at the brass tubes and all else at next opportunity.

I had been wondering about the condition of the reverb pan itself and just happen to have a brand-new Accutronics reverb pan 4AB3C1C (vertical mount version) that I purchased for a different project - building a Surfy Bear reverb unit, which is a solid state FET-based 6G15 equivalent circuit that has gotten great reviews on some of the surf music forums out there. Not to be a heretic but I am desperate to own a good reference unit to know if I have really worked the kinks out of my real 6G15. Part of my plan is to temporarily swap in this new pan and although I know it will sound a little different being a different make etc. it will at least help rule out any shortcomings in the vintage pan.

I'd read that reverb pans can be repaired for $40 or so but not sure were to take it and what is involved - if transducers are replaced, does that potentially alter the sound anyway?


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 12:10 pm
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Stoopy wrote:
I'd read that reverb pans can be repaired for $40 or so but not sure were to take it and what is involved - if transducers are replaced, does that potentially alter the sound anyway?


Yes, there used to be an Ebay vendor who specialized in the repair of vintage Gibbs and Hammond tanks (only those two types) but I haven't seen the listing in quite some time. He repaired two vintage Gibbs units for me and I was quite pleased with the results. From e-mail exchanges I had with him, he replaces only those components that require it and recycles everything else. He charged forty bucks per tank plus S&H.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 12:32 pm
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Stoopy, you may want to try the tank you have, first --- after replacing the non-OEM two parallel resistors on the 6K6GT cathode with a 1k-ohm, 5 watt (or 3 watt) resistor. I'm pretty sure any weak tone is prolly due to poor biasing of that tube.

The 6K6GT is the reverb tank driver (similar function as the 12AT7 reverb driver in most Fender amps). And the current setup is not correct.

Arjay, good reference! Thanks!


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 1:50 pm
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BMW2002Ti wrote:
Arjay, good reference! Thanks!


Doh......I think it was *you* who e-mailed it to me, a couple of years ago.

:wink:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 6:04 pm
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Great thread Stoopy.
I have been looking for one of these for about 6 months, originals don't come around often in my price range.


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 6:35 pm
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Retroverbial wrote:
Doh......I think it was *you* who e-mailed it to me, a couple of years ago.

:wink:

Arjay



Oh Good Grief! Forgot to take my meds! Wait, I forgot what meds they were? :?: :lol:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 6:54 pm
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BMW2002Ti wrote:
Stoopy, you may want to try the tank you have, first --- after replacing the non-OEM two parallel resistors on the 6K6GT cathode with a 1k-ohm, 5 watt (or 3 watt) resistor. I'm pretty sure any weak tone is prolly due to poor biasing of that tube.

The 6K6GT is the reverb tank driver (similar function as the 12AT7 reverb driver in most Fender amps). And the current setup is not correct.

That is indeed the very plan. I get a little OCD particularly when stepping into new waters but also since there multiple items needing attention or improvement, I made the below plan of attack and priorities with parts as specified. I'll be ordering them and then will report back once stuff arrives and I start soldering. I already have a Sprague Atom 250 ufd / 25V which matches the spec so might use that over on the 7025 bypass instead of a longer-life 50V version, at least to start with. Will get higher rated caps for 6K6 and 12AT7 bypass positions.

Even though those caps may not "need" replacing I agree with previous comments about that type of part being in this type of amp and the bottom line is a more "proper" axial cap is just gonna be cooler. And if it's cool it's worth doing. Hopefully if I've listened correctly, all the below is correct.

Image

sfceric64 - glad you like the thread and I too am digging all the great stuff being brought up here. Best of luck on your search!


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Thu Mar 02, 2017 7:40 pm
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Stoopy, well organized! The 10k-ohm wire-wound "cement brick" resistor in my PSU supply is a 5-watt wire-wound. I like WW in the PSU.

Also, I recommend the bypass cap on the 12AT7 = 25mfd/50VDC. The new 50VDC rated caps are tiny and will give you some voltage headroom. Esp nice, with today's higher outlet voltages. Mine hits 125VAC, at times.

There are no 50VDC rated 250mfd caps that I know of... So, go with the 25VDC rated one.

One other thing... it looks like the previous owner swap out a ceramic disc cap 250 pico-farad cap with a silver mica one (green elongated blob between the TONE and MIXER controls). This is a critical coupling cap. I also, replaced this (0.00025mfd = 250 pico) cap. Makes a BIG difference in clarity of tone. If in doubt replace with 250 pico-farad, 500VDC or higher rated silver mica cap.


Looks like the Reverb Unit is in good hands. Well worth the effort of doing the fixes complete and correct.

Good luck!

:mrgreen:


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Sat Mar 04, 2017 4:08 am
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Stoopy, you might find this useful......

http://www.ebay.com/itm/Vintage-Gibbs-S ... Sw32lYriDl

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Some TLC for my 1965 6G15 Reverb Unit
Posted: Sun Mar 05, 2017 8:09 am
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Retroverbial wrote:
Stoopy, you might find this useful......

http://www.ebay.com/itm/Vintage-Gibbs-S ... Sw32lYriDl

Arjay


Thanks for the heads-up Arjay! Very tempting to jump on that for the price. I am not sure of it's configured for mounting on its side like the ones used in these Fender units, I get the impression it's made to be mounted flat, judging by the grommets. And I am wondering if the listed output impedance is right for this application? Having read the Accutronics info and looking at replacement reverb pans that always specify the "4AB" type, seems to imply that input should be 8-10 Ohms and output should be 2250-2575 ohms. The latter being much lower than what this seller specs that pan at. I don't know how meaningful that could be or if I'm treating the Accutronics info too authoritatively.

Sure is tempting though eh? I need to step carefully right now as I've been ordering a buncha stuff for this project as well as for the Surfy Bear reverb unit I am building and Mrs. Stoopy is making some worrisome grumbling noises every time she sees a new PayPal invoice show up in our email. :)

Best Regards - Erich


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