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All 7 pin tube amp—Video DemoClips Added 1/27/18
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Re: All 7 pin tube amp
He who dies with the most tubes... wins
- RJ Guitars
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Re: All 7 pin tube amp
Very nicely done. thanks for posting this up! I really like 7 pin tubes although there are really very few options for high gain 7 pin preamp triodes. I think most all-7-pin designs never caught on in a big way once high gain twin triodes were available in a 9 pin configuration. David Root put together a few amps using the 6AK5 pentode in the first gain stage and EL91's in the output stage... One great deception in all this is that a pair of 7 pin pentodes in the output stage can really put out some volume. Thanks again.
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- martin manning
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Re: All 7 pin tube amp
If you really want 7-pin, 6AV6 is same spec as 12AX7 triode.
Re: All 7 pin tube amp
Thanks RJ.
Yeah, ~10 watts can be quite loud. Honestly, loud is not really something that I need. I like manageable volume levels and only really need to fill a small room... I'm no rock star. You're right though, there seem to be few high gain triodes available. Luckily, this amp doesn't require any. And, the 5725 seems to be a good inexpensive pentode. When the overtime checks start coming in, I plan on buying some more 6AQ5's to try and roll a few through.
I'm still intending to try a few tweaks optimize the VVR and PA bias.
I've also thought about messing with the pre amp pentode screen voltages to see what effect it might have. Perhaps, raise the screens on the first and lower on the second(?), or vise versa--Does any body have an opinion on such an arrangement?
Yeah, ~10 watts can be quite loud. Honestly, loud is not really something that I need. I like manageable volume levels and only really need to fill a small room... I'm no rock star. You're right though, there seem to be few high gain triodes available. Luckily, this amp doesn't require any. And, the 5725 seems to be a good inexpensive pentode. When the overtime checks start coming in, I plan on buying some more 6AQ5's to try and roll a few through.
I'm still intending to try a few tweaks optimize the VVR and PA bias.
I've also thought about messing with the pre amp pentode screen voltages to see what effect it might have. Perhaps, raise the screens on the first and lower on the second(?), or vise versa--Does any body have an opinion on such an arrangement?
Re: All 7 pin tube amp
Thanks Martin, I've had trouble acquiring 6AV6's and this build was all about the pentodes.
- martin manning
- Posts: 13356
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Re: All 7 pin tube amp
You could play with Blencowe's morph control, which transitions from pentode to triode.
Re: All 7 pin tube amp
I have an amp I built that has a paralleled 12ax7 input > TB tone stack > 6sj7 w/a VVR to control only the screen voltage > parallel 12au7 cathodyne > cathode biased 6v6's.
Changing the screen voltage has a pretty noticeable effect. At higher voltages it seems to be more glassy and lively and lower voltages more velvety and compressed.
If I were to make the two pentode stages dissimilar, which way do you think would be more desirable?
Changing the screen voltage has a pretty noticeable effect. At higher voltages it seems to be more glassy and lively and lower voltages more velvety and compressed.
If I were to make the two pentode stages dissimilar, which way do you think would be more desirable?
Re: All 7 pin tube amp
Turn one of them into a triode/pentode morph control - whichever one that doesn't have a significant AC load after it.
He who dies with the most tubes... wins
Re: All 7 pin tube amp
Plugged in this evening and cooler whether in No Cal had the AC voltage coming in at 121-122v and this pushed the plate to cathode voltage up to 251-253v--just over the stated limit--probably not an issue. So, I will leave the VVR's max limiting resistor as is.
I tried the cathode bias redistor at 150//330r=103r and dissipation was at 105%. Maybe, I should order a 120R resistor. Although, it's probably safer as is.
Also, it seems a bit tight. Do you think changing to 10uF filter caps in the pre and PI nodes (as in the original Gibson schematic) would be beneficial? Maybe it isn't so tight that it needs a change.
I did notice that it will squeal a bit when both gain and tone are dimed, dependent upon guitar proximity. I think I might add a grid stopper to the second gain stage which would have no resistance if both knobs are full on at "10".
I tried the cathode bias redistor at 150//330r=103r and dissipation was at 105%. Maybe, I should order a 120R resistor. Although, it's probably safer as is.
Also, it seems a bit tight. Do you think changing to 10uF filter caps in the pre and PI nodes (as in the original Gibson schematic) would be beneficial? Maybe it isn't so tight that it needs a change.
I did notice that it will squeal a bit when both gain and tone are dimed, dependent upon guitar proximity. I think I might add a grid stopper to the second gain stage which would have no resistance if both knobs are full on at "10".
- Kagliostro
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- Location: Italy
Re: All 7 pin tube amp
Please can someone post a link to David Root amp with 6ak5 ?
Thanks
K
Thanks
K
-
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Re: All 7 pin tube amp
Beautiful built right there!
Very interested in doing some 7-pin project myself.\
The EC91/6AQ4 is a high mu single triode, anyone use these before?
Edit: For a pentode pre, how about the 12AU6? Probably one of the few 7 pin tubes that have been used in guitar amp design (Kay, Silvertone)
Very interested in doing some 7-pin project myself.\
The EC91/6AQ4 is a high mu single triode, anyone use these before?
Edit: For a pentode pre, how about the 12AU6? Probably one of the few 7 pin tubes that have been used in guitar amp design (Kay, Silvertone)
Re: All 7 pin tube amp
Thanks bluesbreaker62.
I am quite pleased with the way it came together.
I am quite pleased with the way it came together.
Re: All 7 pin tube amp
Another cool use of chokes is the Gibson GA-90 where Seth Lover used a choke in the preamp to silence single coil hum. Worked like a charm too, the amp has a great warm clean sound. Scotty Moore used one for a while and it has this unique qty 6 of 8" speaker config too. Overall the amp is too early/clean to even get into blues territory - something the GA-40 doesn't have issue with, but it's a fun concept to incorporate into designs especially for P90's and strat/tele's.
https://elektrotanya.com/PREVIEWS/63463 ... .pdf_1.png
I'm also in norcal - nice to get a break from the oven we've been having!
Cool build!
https://elektrotanya.com/PREVIEWS/63463 ... .pdf_1.png
I'm also in norcal - nice to get a break from the oven we've been having!
Cool build!
Re: All 7 pin tube amp
Thanks gtomax,
Wow, that is a crazy circuit. Thanks for posting.
Is that inductor part of a tone circuit?
Looks like a cathodyne PI followed by a gain stage?
I like the cooler weather this week too.
Wow, that is a crazy circuit. Thanks for posting.
Is that inductor part of a tone circuit?
Looks like a cathodyne PI followed by a gain stage?
I like the cooler weather this week too.
Re: All 7 pin tube amp
This might be it -- http://ampgarage.com/forum/viewtopic.php?t=28239Kagliostro wrote: ↑Fri Sep 08, 2017 6:33 am Please can someone post a link to David Root amp with 6ak5 ?