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Vintage threads from the first ten years

Ampeg 7591 to 6v6

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1/7/2000 9:05 PM
Jim	Ampeg 7591 to 6v6 Need a detailed description on how to do this. Can anybody help?

1/7/2000 10:11 PM
steve m	Jim, I know this isn't exactly what you're after but check out this link: http://triodeel.com/7591.htm It details converting an amp to use 6l6 tubes rather than the 6V6. Hope this helps, Steve

1/10/2000 5:26 PM

The only "problem" with converting one of these old ampegs to use 6L6 or 6V6 is that it will change the tone of the amp. Been there, done that. I once converted an old Reverberocket to 6L6, and an old Super Echo Twin to 6V6. In retrospect, I would today urge the owners to stay with 7591s as long as they could possibly afford them. In addition to the socket re-wire, you have to change the cathode bias resistor, and I would additionally recommend you replace the cathode bypass cap with one rated for 50 Volts.

1/10/2000 8:57 PM

John- I am interested in your opinions on "how" the tube change affected the tone. I got a Gemini VI this summer and immediately replaced the Sovteks with Svet 6L6's, because I use the thing a lot and plan to retube every 6 months. I didn't want to be limited to the Sovteks or very expensive NOS. I love the sound of the amp, and having owned a VT-40, I still hear the ampeg character. As you no doubt know, they made Jets with 6v6's and B-15's and 518's with 6L6's. To tell you the truth, the most crucial change I made was to replace the Sovtek 7199 with a NOS Sylvania!

1/10/2000 10:27 PM

Jaye, isn't the Gemini a fixed-bias amp? If so, then I don't think you'll suffer as much hit. Recall that like the EL84, the 7591 requires very little grid bias voltage. Hence, it can develop full power with relatively little grid drive. In contrast, the 6L6 requires much greater grid drive voltage to get up to full-tilt. This will effectively reduce the overall gain of the amp. The 7591 seems to have a characteristic sound all it's own, just like the 6V6, EL84 etc. are associated with certain sonic properties. I really like the sound of those things with 7591s installed. The Reverberocket I converted just seemed to lose presence and punch. Mind you, I'm not saying it sounded *bad*, just different.

1/11/2000 1:54 AM
Sideways Jaye	John- You are correct sir, the Gemini is fixed bias (and ss rectifier). I follow what you are saying. Also, it's not like I had premium NOS 7591's in there to begin with.

1/11/2000 4:41 AM

john stokes wrote:
<< Been there, done that. I once converted an old Reverberocket to 6L6, and
an old Super Echo Twin to 6V6.>>

hi john,

of course the first versions of the Echo Twin
used 6V6s originally--
but i understand your point
about 7591s having a tone of their own.
my Gemini I w/ 7591s
can compete strongly with a DR!

regards, bill

p.s. all of y'all, as i say after 20 years in NC,
if you haven't seen our AMPEG book please check:
http://members.aol.com/risehigh/book.htm

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