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Post subject: Re: BF SR problem(s)
Posted: Fri Apr 20, 2012 10:12 pm
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Boy, it sure helps to walk away from amps sometimes and come back with a fresh view. First, thanks for all the 100K/100K and 82K/100K discussion. Really interesting, as this and the 220K-ohm grid-to-ground resistors are the only 5% tolerance ones OEM in the amp. And yes, there are 1.5k-ohm grid stoppers on the 6L6GC's, in this amp.

Thanks, for the 4.7k-ohm and 1kohm suggestion in the PS rail. Yes they are the original parts and placed correctly. The caps have all been replaced before with Spragues. But, I believe there inlies the problem. NORMAL louder than VIBRATO channel. And a definite slight hum with every tube pulled except the rectifier and output tubes (yes I tried different tubes). My guess is one of those 20mfd/500VDC caps has gone South. So redo the PS train and report back.

As for the input... that was a big dead end. I was not thinking clearly at 2am (or whenever it was). Thinking stricly input issues and totally forgetting about the power supply.

I got that Ampeg Jet in. Oh man what a beauty! Just needed new 7591A (luckily, I have a stash of Westinghouse made). Cap can & cathode-resistor. The amp is around the size of a Princeton Reverb. But, the TONE! Bright and shimmering. Thank goodness it wasn't a big fix.


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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 12:24 am
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That's good news about the Ampeg! Knew you'd ferret out the channel level situation, on the Fender. Sometimes, those breaks make the difference! JMO Art

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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 1:02 am
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aclempoppi wrote:
Sometimes, those breaks make the difference!


Indeed.

Now how about some pics of that Jet......?

8)

Arjay

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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 1:19 am
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Guys, the Ampeg is a KILLER amp! I'm taking the back off (those crazy screws that Ampeg uses) and who do you think worked on it last? Jess Oliver! His signature, date (2005). Just needed very little.

Will gets some photos tomorrow or Sunday.


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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 4:28 pm
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Some early photos of the Jet:

Image

Image

Image

Image

Image


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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 6:14 pm
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That is a heck of an idea...putting the schematic on the back panel :idea: :!:

Nice amp too...kind of odd tubes though...or is my noobness showing?

T2

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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 6:21 pm
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Ampeg often followed an alternate path when it came to tubes and Ampeg owners paid the price when many of those obscure bottles went OOP in the early '80s (the sad saga of the 7027A and the myriad V4's, VT22's, B25B's, etc, that used them is an excellent example). The original SVT was not designed around 6550's and the only reason it survived these 4+ decades is because someone at Magnavox had their thinking cap on and forced a revision using a common power tube prior to the start of production.

Arjay

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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 6:30 pm
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T2 and Arjay,

The 7591A is a GREAT tube! I have a bunch of Westinghouse stashed just for when one of these or a ReverboRocket comes in. If you rebased the amp to take the 6V6GT, it'll work fine--- but loses the "Ampeg" tone. That shimmering, bright, tremolo-pack tone.

But those compactrons! Now, those are really hard to find. I have some from an USAF surplus base I bought awhile back. There was one Fender (post SF era) that used a 6K11 or 6Q11, if I remember correctly.

Anyhow, put a Weber 12F150 into this puppy and it simply took off. Will run it against my BFPR tonight. Outta be fun!


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Post subject: Re: BF SR problem(s)
Posted: Sat Apr 21, 2012 6:36 pm
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Neat amp, Beemer! Art

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Post subject: Re: BF SR problem(s)
Posted: Mon Apr 23, 2012 12:06 pm
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Cool looking components in that amp....I might have some of the 6BK11s in a box....I'll check.


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Post subject: Re: BF SR problem(s)
Posted: Mon Apr 23, 2012 8:20 pm
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kk.. cool. Those 6BK11 really pump up the vibrato/tremolo section. This amp have as sweet and powerful a tremolo as my 1962 Pro (which runs 3 x 12AX7 to drive that circuit).

With Weber 12F150 (1000% improvement over MII Jensen RI P12R). Mated to modded '63 RI Reverb Unit = deliciously dripping wet, swooshie tones.

Image

Image


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Post subject: Re: BF SR problem(s)
Posted: Tue Apr 24, 2012 7:05 am
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BMW2002Ti wrote:
'63 RI Reverb Unit = deliciously dripping wet, swooshie tones.


I needs me one of those. I love that reverb driven surf tune sound.

Arc

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Post subject: Re: BF SR problem(s)
Posted: Tue Apr 24, 2012 8:36 am
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I have both an original 1966 6G15 Reverb Unit and the '63 Reissued one. The RI does not come close to the original, in terms of depth and fine tuning the 'verb tone. I did modify the RI to get as close to the 6G15 as possible. Simple start is a good tank in place of the Korean made one (I had a old Cary, IN made one out of a BFPR era amp). And a strong testing 6V6GT (maybe even a selected JJ-6V6S).

You can work with the guts. But, need to be very careful of the delicate circuit board and tracings. Silver mica cap in place of the ceramic 250 pico-farad and new quality power supply filter caps (I used F&T), brings the unit to life and helps the top end response, a lot.

I did much more modifcations. Coupling caps, etc. Each mod helped a little more to get the RI back to 6G15 standards. IMHO.

If you buy a '63 RI Reverb Unit and are interested in all the modifications I did, I can can email or post them.


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