Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jojokeo on June 26, 2018, 04:23:15 pm
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I don't have much experience with octals so for all you older
farts dudes out there, is there much difference between these two tubes? An amp example would be the Matchless Clubman 35 that uses the SH7 as a recovery tube.
1) Is it slightly lower gain or less microphonic than the SJ7?
2) The SH7 was replaced by the 6AU6, 6AK5, etc... any reason/guess why the octal was used over the more modern pentodes available?
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I suspect at some point the 6SH7 was over-produced and then sold at clearance price. It pops up many places you would not expect it.
The datasheet does NOT want you to use it in high gain audio because it may hum. Clearly this didn't bother some amp factories; either it wasn't as bad as the sheet said, or some less than others, or what's a little hum in a guitar amp (pickup coils absorbing hum from the air on the stage)?
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Although I have occasionally worked on octal tube amps I have yet to build an amp to use one. It just seems a bit dicey and asking for possible trouble where it's why tempt Mr Murphy to come out of the closet? I prefer to try to keep him shackled in the dungeon where he belongs.
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Although I have occasionally worked on octal tube amps I have yet to build an amp to use one. It just seems a bit dicey and asking for possible trouble where it's why tempt Mr Murphy to come out of the closet? I prefer to try to keep him shackled in the dungeon where he belongs.
You know Joe, I have heard all the things relating to the horror stories, but since I began this hobby with old radios, the old tubes along with using the chassis for filiment circuits seemed to work fine. Of course the wooden knobs kept Murphy's shock at bay. Old Organs gave me
Sort of like the Wright Brothers, since they did not believe man couldn't fly, they did. My Uncle, 1 up was a failure with his soft drink recepie 6 times. :l2:
Cascode a 6SN7 or use a 6SL7 for a gain andor recovery stage. Most people say they do not sound any different. Just like a little EL84 sounds just like a 6L6 you now. :help:
Oddly enough I have never had one go microphonic, even the 6SJ7. These are not new production I am speaking of and have no experience with new production. I know someone with a few that could send you one and it wouldn't take as long as getting a Linear Boost. Kidding, maybe?!
BTW, you are older than me so that makes you an old fart.
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I have yet to build an amp to use one
I'm contrarian by design, :icon_biggrin:
so when I got here everyone loved 12-something, so I played with all the octals I had, even some 4 pin'rs, anything BUT a 12AX7 :laugh:
the 6SN7 seemed to perk to the top, (old stock, and new(EH type)). It's just laid back, not prissy like hi-gainers. It seems to bend and flow however I use it, rather than bark n bite. I have typically used it as a driver for xSE PA , or V1.
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Are they that bad with noise? I'm just curious because I plan on using them in one of my future projects and I don't think I remember hearing a lot of anything bad about them.
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6SN7 seemed to perk to the top, (old stock, and new(EH type)). It's just laid back, not prissy like hi-gainers. It seems to bend and flow however I use it, rather than bark n bite. I have typically used it as a driver for xSE PA , or V1.
That is a good description. Sometimes I read my own writing and realize my mind just meanders. Anyway, it seems like these tubes are still easy to get my hands on too. I bought 9 nice ones at a flea market, some 6SN7 and 6SL7 still in those really cool well made boxes with the metal edge crimps. Different brands, but they were $4 each or 3 for $10. This has something to to with it too, the old advertising.
I have heard some players say when the 12Ax7 came along it sterilized amp tone. I just think it is different and I know Joe likes the pentode preamp tubes, even the small signal ones. Even the transistor, as hated as it is, still sounds cool every time I hear the intro lick to Satisfaction.
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Are they that bad with noise? I'm just curious because I plan on using them in one of my future projects and I don't think I remember hearing a lot of anything bad about them.
Check out Little Walter amps reviews. I have played 2 and both were basically old 5B3 with octals, but with updated components and were quiet sound great to me.
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I use mostly 6SL7 the whole way through the amp and really like them. Some of the Russian NOS can be noisy, but not all of them. The old used RCA, etc. are real nice. Getting them out of reel to reels or record players probably makes a difference; I doubt they have more than a few hundred hours on em.
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I just think it is different and I know Joe likes the pentode preamp tubes, even the small signal ones. Even the transistor, as hated as it is, still sounds cool every time I hear the intro lick to Satisfaction.
Yes indeed! :icon_biggrin: They are quite versatile little gems and germs alike. Most ALL high gain amps contain transistors and op-amps, basically amps combined with pedal circuits premade inside. And nothing wrong with this idea. It's the only real way to get certain high gain tone and performance along with versatility at modest and reasonable expense. Tube tone is cool but great when pushed properly.
I know someone with a few that could send you one and it wouldn't take as long as getting a Linear Boost. Kidding, maybe?!
I have no more reasonable explanations other than unscheduled work continues to flow in in all directions. It's a double edged sword cause despite too many irons in the fire there's Benjamin's flowing into the wallet. The ProBoost, Steel String Special, Blackmore Aiwa Preamp (if Jimbo ever sends it back to me?), & Queen Bee are languishing as constant reminders that they are all ready to go too. And will be soon enough, it's just managing all of the workflow. I can explain all the peripheral stuff offline...
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Are they that bad with noise? I'm just curious because I plan on using them in one of my future projects and I don't think I remember hearing a lot of anything bad about them.
The datasheet mentions hum, I assume they mean 60hz heater hum. Microphonics would be a bigger problem (causing feedback, rattling noise, etc). If you did have problems with hum I think you could avoid it with DC heaters, though that's a lot of effort that wouldn't be needed otherwise.
Other (all?) preamp pentodes do sometimes have issues with microphonics. I think that's why the EF86 wasn't used that much for that long. I'm not sure this one would be any worse, but that doesn't mean it's trouble-free.
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Quite a bit of hum came from the repair, and age of unit working. These tubes seem to have no trouble with elevated to 70 vdc. And I always use humdinger for balance, but since I began doing this I add it to most builds and some repairs.