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Post subject: 70's Deluxe Reverb Problem
Posted: Sat May 26, 2012 9:03 pm
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Hi everyone, 1st post here. and thanks in advance for any and all help.
here's my situation. i have an older 70' deluxe reverb that is supposed to have the blackface specs with 6l6gc power tubes. now here is what is happening it has low output and is distorted "in a bad way" and when playing there is a blue flash in the power tubes as i hit the guitar strings. just so you know the power tubes are new as with the rectifier tube filter caps are only a couple of years old at the most and output transformer is fairly new also. i was only getting about -2vdc at the bias pot. changed out the PI coupling caps,bias pot and resistor. then i was getting up to -28vdc no higher. went back later to check again now it is only getting -18vdc . any guesses as to what might be doing this?


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 12:28 am
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The standard complement of output tubes for a Deluxe Reverb is a pair of 6V6GT's. As for the low bias voltage, you should be seeing -35VDC at the bias pot's wiper. If it shows low, I'd suspect the diode or the 470-ohm 1-watt resistor on the bias board is heading south towards permanent "retirement".

What rectifier tube is installed?

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 7:41 am
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Arjay, I think that the arcing here is a hint of improper output tubes sucking too much current for the heaters and/or plates from the PT. As either the GZ34 or the 5U4GB can drive two 6L6GC, PROVIDED they are attached to a proper PT.

And the low negative bias voltage (-28VDC) is an indication that some tech tried to crank the 6L6GC's into a more desirable idle range. Which is impossible on a stock 6V6GT driven DR.

If those are 6L6GC's and the amp is stone stock, you are very lucky you haven't fried that PT. I'd imagine that you should not only change the output tube back to proper 6V6GT, but you should have the PT, OPT, grid stopper & screen resistors, and the PS rail filter caps and resistors looked at--- for signs of abuse.

JMO. Good luck! That is one amp you want to set straight. It's well worth it.


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 7:45 am
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BMW2002Ti wrote:
That is one amp you want to set straight. It's well worth it.


Indeed!

Fry that OEM iron and it'll take hundreds to replace.

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 10:14 am
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The rectifier is a 5AR4. and i have a solid state replacement on order" thinking that would be better for the 6l6's" .also would a in4007 be a suitable replacement for the bias board diode?

UPDATE : went to check on the filter caps .visually they look fine but i cannot get a voltage reading off of 2 of them, meter just flashes " O.L. " leading me to think they are bad :?


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 12:12 pm
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I think it would be a good idea to first install a set of 6V6's and then take all your readings off of that. That way you know exactly where you stand. If it checks out o.k., then you can proceed to focus on getting the amp working with 6L6's correctly.
Just my opinion,
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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 12:19 pm
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t-rack7 wrote:
also would a in4007 be a suitable replacement for the bias board diode?


A UF4003 or UF4004 would be a better choice.

HTH

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 12:26 pm
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thanks for the advice, I'll get going on some 6v6's and a new diode.


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 12:36 pm
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You might consider re-capping as well with some fresh 16uf/450V Sprague electrolytics. Those readings you measured don't sound too copasetic.

HTH

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 1:08 pm
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OK... to be clear, the 6L6GC requires 0.9amps per tube for its heater line. The 6V6GT requires 0.45amps. That's a total of 1.8 amps versus 0.9 amps. A BIG difference.

You will never see a DR sized PT in a dual 6L6GC amp, just for this reason. You must run 6V6GT tubes in this amp. REGARDLESS of the rectifier. It's the PT (which comes before the rectifier, in the power train), that is your limiting step. NOT THE rectifier. Yours prolly came with a 5U4GB stock. A good rectifier that can power either a dual 6V6GT or 6L6GC amp fine, provided the PT is correct.

That aside, the 6L6GC puts out a lot more current than the 6V6GT. Your OPT is designed to "see" 6V6GT current. Not 6L6GC. You will never see a 6V6GT sized OPT in an dual 6L6GC amp.

If you desire a cleaner tone with a bit more headroom than the typical 6V6GT, try a selected pair of JJ 6V6S. PLease just pull those 6L6GC and replace with proper 6V6GT (or the 6V6S). I'd would really hate to have those precious trannies fry up on you.

In addendum: Many ppl run NOS 6V6GT in 6L6GC amps. No problem. Just rebias and go. But, NEVER run 6L6GC in a 6V6GT amp.

You should have all of the PS rail, bias supply, and output section grid stoppers and screen resistor checked for being overstressed--- in the event those 6L6GC were in the amp for a long time & push hard to "10."

Good luck!


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 1:21 pm
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BMW2002Ti wrote:
OK... to be clear, the 6L6GC requires 0.9amps per tube for its heater line. The 6V6GT requires 0.45amps. That's a total of 1.8 amps versus 0.9 amps. A BIG difference.


+1000!

The old Woodward-Schumacher iron was tough......but I'm not sure it's that tough to tempt fate by overstressing the heater tap by nearly one hundred percent, especially with windings over four decades old.

We didn't understand WTF we were doing back then when we dreamed up all those crazy mods.

But we do now.

:roll:

Leo knew best......and he always did.

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 10:11 pm
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Exactly RJ,it seems the "mod squad" has been turning over a new leaf lately,I don't see as many guys discussing hotrodding vintage amps to get more headroom...I think the risks outweigh the benefits,for amps that are classics in their original design....you said it,Leo knew best. :D
There's a whole lot to be said about 6V6 tone vs. 6L6 tone,each has it's rightful place in many types of music,and there's many amps to choose from without trying to make one amp into another.


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Sun May 27, 2012 11:52 pm
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Rebelsoul wrote:
There's a whole lot to be said about 6V6 tone vs. 6L6 tone,each has it's rightful place in many types of music......


+1

I'd even cede the point that other power tubes produce their own distinct (and pleasant) tone -- such as the EL84, the 7027A, and the mighty 6550. They're just not the traditional "Fender" tone. Most of us appreciate the chimey vibe that Tom Petty drives from his vintage AC30TB, Tom Johnston's smooth-and-ballsy bite on China Grove, or the sonic thunder that Keef let loose on the Git Yer Ya-Ya's Out album. But nothing sounds quite like a Leo-designed Fender with either 6L6's or 6V6's......legendary tone that's first among equals.

Arjay

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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Mon May 28, 2012 7:37 am
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I know a couple musicians locally that like to run 6L6s in their DRs, never understood why... I like the DR tone because of the 6V6s in there and would never consider doing that myself. I have 3 DRs and I'm extremely happy with 6V6s in there! If I want more clean headroom I'd replace the speaker.

For a bigger and cleaner 6L6 tone I turn to my SR :)


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Post subject: Re: 70's Deluxe Reverb Problem
Posted: Mon May 28, 2012 8:10 am
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That's right Cedar,people who are serious about vintage tone and getting the most original tone possible,sometimes means owning more than one amp,especially if you're trying to gig with them and fit the room....it's hard to get "the one"...but the Deluxe Reverb is really close to being that one!


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