Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ernie_jr on October 22, 2012, 06:59:41 am
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Has anyone used 7591 tubes? I have a few sets from a scraped fischer amp that I inherited from my dad?
Thanks,
Ernie
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They are pretty common in high fidelity applications and even some guitar amps (ampeg comes to mind). They are great tubes, repinned 7868's really. Nothing wrong with them at all except that they are a little expensive.
They are looking for a an OT with a little bit higher primary impedance than a 6L6.
Dave
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I have an Ampeg Reverberocket 2 that uses a pair of them. Several other 60s Ampeg models use them. I built a single ended amp using a 6GM5 which is the same tube with a different base. They're good.
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One of my amps is a dumble type preamp and phase inverter into cathode biased push pull 7591 power tubes. It is very robust sounding, with more clean volume than a Fender deluxe reverb. The power tube circuit and transformers are taken from an old Eico Stereo 40 hi-fi amp.
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One of my amps is a dumble type preamp and phase inverter into cathode biased push pull 7591 power tubes.
That sounds like a cool amp! Interesting idea.
With respect, Tubenit
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Thanks Tubenit. I was lucky that it worked, and actually sounds good. It is a classic case of cut and paste amp design. I do not actually know what I am doing.
But getting back to the original question, if you have some good 7591's, I would say it is well worth building an amp with them. But if its a matter of buying new production tubes, 6L6 and 6V6 types are priced lower, and I'd probably stick with those.
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I built a princeton reverb type circuit using 7591's.I think it sounds great.Its very loud Definately more headroom than 6v6's.
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7868/7591's are my favorite power tubes. Powerwise, they are in between a 6V6 and a 6L6GC. Soundwise, they are similar to an EL84 in that they have a lot of gm for a power tube so it doesn't take much to drive them, and when you do, they are juicy and harmonically rich sounding. They sound more like 6V6/6L6GC than EL84's except for the smoother distortion characteristic of the EL84's, so they are very versatile. They are touch responsive too, though that depends on your amp configuration also. They like around a 6k6 load from the OT. They do fine with power scaling also, though you have to run the screen close to the plate to get the best performance from power scaling so you have to make sure your voltages aren't too high. I'm actually running mine over the recommended screen voltage in a Bogen build using the EH 7868's (which sound as good or better than NOS ones) and they are holding up just fine.
If JJ was smart, they would issue a version of their 7591 with a standard pinout. Then all the guitar players would have a middle option between the 6V6 and 6L6 that they could try.
Greg
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I thought that's what they already were with their 6V6's. The insane voltages those 6V6s can take make me wonder if that's what they are. :undecided:
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I thought that's what they already were with their 6V6's. The insane voltages those 6V6s can take make me wonder if that's what they are. :undecided:
Ya their 6V6 can take high voltages for sure! The 7591 is a power tube with more gain though, so while its power output falls between a traditional 6V6 and a 6L6GC, it has more gain than both so it doesn't need much of a preamp to drive it, and when you do drive it, it tends to be more harmonically rich sounding than either of the other two. The thing that holds the 7591 back aside from the expense is it's odd pinout, so if they got the same pinout as the 6v6 and its ilk, then a lot of guitarists would be interested if they got the word out. It would be cheap for someone like JJ to try and see!
Greg
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> 7591 with a standard pinout. Then all the guitar players
Higher gain means much less bias, or on the same bias running stone-cold.
You guys can figure it out, but "most" guitarists would not have a clue how to use 7591 properly in 6V6 sockets.