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Old 5th February 2013, 06:11 AM   #1
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Default Question regarding 7199 Tube wiring

A friend brought in an old console stereo SE power amp he retrofitted with a 500k dual gang volume pot and a pair of RCA signal input cables.

The amp utilizes a pair of 7199 tubes feeding a pair of 7408 (6v6 variant) output tubes.

He had the vol pot inputs 1 and 2 going to their respective positive L and R RCA signal input wires.

And he wired volume pot wiper 1 to Pin 9 of one 7199 tube and wiper 2 to Pin 9 of the other 7199 (which according to my pin-out chart for this tube are the grids for the Triode portion of this tube)

The grounds from the volume pot run back to the common chassis ground at the signal input grounds of L and R RCA inputs.

The problem is that although the amp produces output the signal shows minimal increase in gain then max at about the 1/4 position and remains constant from the 1/2 position to 3/4 position and then cuts out completely at the max position.

I disconnected the volume pot from the amp while feeding it a signal from a CD player with variable output and all is well. Amp sounds great and performs as it should.

Checked the resistance of the pot and it too checks out at 478 ohms - 0.

My question is that I notice the 7199 tubes in this amp are bridged between pins 2 (Pentode plate) and pins 7 (Triode Grids). Does this seem correct?

If it is...then where exactly does one run the wires from Wipers 1 and 2 from the volume pot to on the 7199s in order to properly implement a volume pot?

Thanks. Leon
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Last edited by devilsindetails; 5th February 2013 at 06:18 AM.
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Old 5th February 2013, 09:46 AM   #2
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The wipers need to go to the grids of the pentodes. The plate is directly coupled to the triode grid, which you should leave alone.

See the RCA tube manual for schematics of this very common arrangement.
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Old 5th February 2013, 01:07 PM   #3
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Single-ended amp with 7199? Only one I know is the Stromberg Carlson ASR-110. If that's it, see my page for a schematic: Made In Rochester
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Old 5th February 2013, 01:56 PM   #4
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Thanks gentlemen...that clears up the matter...I really only have a little experience with 12A_7 variety pre-amp stages so the wiiring of the vol pot on this kind of threw me...

Yes...I checked with my friend and it did, indeed, come from a Stromberg Carlson console of some kind....thanks again, Leon
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Last edited by devilsindetails; 5th February 2013 at 02:05 PM.
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