richwalters said:
Richj, your "over-exposed" is much better than most of "well-protected". I am guilty as well of fashion-like designs when tubes are exposed, but I have to admit that it is a good idea to protect tubes from users and users from tubes. I even put ignition keys on my last amps that use GU-50 tubes with 760V inside of breakable sharp glass, so owners can lock them from say children or dummies.
diegot said:
The 6EM7 performs well as a voltage regulator, Vak can drop quite low which is a good thing in this application.
According to the data sheet for 6EM7 max Vhk is +100/-200V. I elevated the heater to +140V so Vhk is here +60/-150/. I suppose that is within the Vhk specifications.
Jan E Veiset
Le Renard
Earlier tonight, I was finally able to complete the construction of my new project: a nearly 40W monoblock based on PP 6BQ6s -- a TV horizontal deflection VT. Here it is in action as I was doing some o'scoping to check out the performance. Here's the data collected:
DC:
Vpp= 352Vdc (350 Design)
Vsgsg= 150Vdc (150Vdc Design)
Vkk= -275Vdc (-300Vdc Design)
Open Loop:
f(h)= 35.7KHz (-3.0db(v); 8R)
f(l)= 16.6Hz
Avol= 55.56 / 8R (55 Calc)
12db(v) gNFB:
f(h)= 50KHz
f(l)= 11Hz
I'm running the finals a bit "hot" here: Ik= 70mA, as opposed to the design value of 30mA. Being that these are HD VTs, they're a good deal tougher than the usual audio finals. Despite some 22W of plate dissipation (6BQ6s are nominally rated at Pd= 12W -- same as a 6V6 -- try that with a 6V6
) there was no trace of any red glow on the finals when viewed in the dark. They held up just swell for two hours' worth of listening time. (I still have a bit of clean-up: get rid of that yellow tag on the OPT and touch up a bit.) I do like the retro look of that bias adjust. meter 
Forch, mounting the chassis in the cabinet didn't disturb anything, and so no unexpected instabilities showed up. Sound remained just as good as it did during the initial round of listening tests before the cabinet was completed. That, I made from red oak, and gave it several coats of Formby's tung oil to bring out the shine. May not be the prettiest, but then again, I'm an engineer, not a carpenter, dammit! I had another thread about this project Here
As for the listening test, when run with no gNFB at all, there is a surprising lack of the expected pentode nastiness. It only becomes obvious when you play it way too loud anyway. There is, however, the usual sloppy bass, due to lack of woofer damping, and excessive "edginess" in the upper mids and highs. Dialing in the full 12db(v) of gNFB, all trace of sloppy bass and pentode nastiness disappears. Hard rock (Nirvana, Foo Fighters, Ozzy) and techno seem a bit "subdued". This might be all right for a production amp, and suits some forms of music (Karen Carpenter, Andre Rieu) just fine. However, backing off to about 6db(v) of gNFB lets Ozzy really "come alive" without sloppy bass, or pentode nastiness and adds just the right amount of edginess. For any sort of hard rock or bass-heavy techno, less is definitely better. You don't get the sloppiness, but bass still packs plenty of "authority". More listening tests to follow, but not right now. The nearly 40W I'm getting will really wake up the neighbours, and I doubt they'd appreciate that.
There is just a trace of 60Hz hum on the output. No way to tell how much since the 50KW AM BCB station 30 miles to the north fills the o'scope screen with its modulation, so I can't tell, but it doesn't seem to amount to more than 5mVp-p. You can barely hear it with your ear right up to the speeks.
Main Schemo
Screen Regulator (Finalized)
Main Power Supply (Finalized)
Earlier tonight, I was finally able to complete the construction of my new project: a nearly 40W monoblock based on PP 6BQ6s -- a TV horizontal deflection VT. Here it is in action as I was doing some o'scoping to check out the performance. Here's the data collected:
DC:
Vpp= 352Vdc (350 Design)
Vsgsg= 150Vdc (150Vdc Design)
Vkk= -275Vdc (-300Vdc Design)
Open Loop:
f(h)= 35.7KHz (-3.0db(v); 8R)
f(l)= 16.6Hz
Avol= 55.56 / 8R (55 Calc)
12db(v) gNFB:
f(h)= 50KHz
f(l)= 11Hz
An externally hosted image should be here but it was not working when we last tested it.
I'm running the finals a bit "hot" here: Ik= 70mA, as opposed to the design value of 30mA. Being that these are HD VTs, they're a good deal tougher than the usual audio finals. Despite some 22W of plate dissipation (6BQ6s are nominally rated at Pd= 12W -- same as a 6V6 -- try that with a 6V6
) there was no trace of any red glow on the finals when viewed in the dark. They held up just swell for two hours' worth of listening time. (I still have a bit of clean-up: get rid of that yellow tag on the OPT and touch up a bit.) I do like the retro look of that bias adjust. meter Forch, mounting the chassis in the cabinet didn't disturb anything, and so no unexpected instabilities showed up. Sound remained just as good as it did during the initial round of listening tests before the cabinet was completed. That, I made from red oak, and gave it several coats of Formby's tung oil to bring out the shine. May not be the prettiest, but then again, I'm an engineer, not a carpenter, dammit!
I had another thread about this project HereAs for the listening test, when run with no gNFB at all, there is a surprising lack of the expected pentode nastiness. It only becomes obvious when you play it way too loud anyway. There is, however, the usual sloppy bass, due to lack of woofer damping, and excessive "edginess" in the upper mids and highs. Dialing in the full 12db(v) of gNFB, all trace of sloppy bass and pentode nastiness disappears. Hard rock (Nirvana, Foo Fighters, Ozzy) and techno seem a bit "subdued". This might be all right for a production amp, and suits some forms of music (Karen Carpenter, Andre Rieu) just fine. However, backing off to about 6db(v) of gNFB lets Ozzy really "come alive" without sloppy bass, or pentode nastiness and adds just the right amount of edginess. For any sort of hard rock or bass-heavy techno, less is definitely better. You don't get the sloppiness, but bass still packs plenty of "authority". More listening tests to follow, but not right now. The nearly 40W I'm getting will really wake up the neighbours, and I doubt they'd appreciate that.
There is just a trace of 60Hz hum on the output. No way to tell how much since the 50KW AM BCB station 30 miles to the north fills the o'scope screen with its modulation, so I can't tell, but it doesn't seem to amount to more than 5mVp-p. You can barely hear it with your ear right up to the speeks.
Main Schemo
Screen Regulator (Finalized)
Main Power Supply (Finalized)
Jane,
I have a question about dc on heaters; something you could easily try (or have tried) in your amplifier. Have you investigated what the audible advantage is?
This is an honest question, not criticism. One often finds quite expensive dc heater supplies (at the cost of components in RSA yours would be moderately expensive) which, when I tried them, gave no audible improvement in hum suppression. (Actually meaning that it was inaudible even with ac on heaters, particularly in power amplifiers.) Sometimes the switching transients are more audible as slight buzz (because of insufficient filtering) than influience of ac.
Thanks
I have a question about dc on heaters; something you could easily try (or have tried) in your amplifier. Have you investigated what the audible advantage is?
This is an honest question, not criticism. One often finds quite expensive dc heater supplies (at the cost of components in RSA yours would be moderately expensive) which, when I tried them, gave no audible improvement in hum suppression. (Actually meaning that it was inaudible even with ac on heaters, particularly in power amplifiers.) Sometimes the switching transients are more audible as slight buzz (because of insufficient filtering) than influience of ac.
Thanks
Well its nowhere near as good as some of these beautiful creations I have seen on here, but here is my restored Magnavox amp 83.
http://getchellaudio.googlepages.com/amp0.JPG
http://getchellaudio.googlepages.com/IMG_0525.JPG
http://getchellaudio.googlepages.com/IMG_0526.JPG
The 6BQ5's are mullards, the 6EU7 is a sylvania, and the 6CA4 is some japaneese brand. These little amps are fun to restore, as the chassis is made of aluminum and polishes up nicley!
I stripped the transformer with strip-ez and repainted it. I see a lot of these restored and no one touches the power transformer.
http://getchellaudio.googlepages.com/amp0.JPG
http://getchellaudio.googlepages.com/IMG_0525.JPG
http://getchellaudio.googlepages.com/IMG_0526.JPG
The 6BQ5's are mullards, the 6EU7 is a sylvania, and the 6CA4 is some japaneese brand. These little amps are fun to restore, as the chassis is made of aluminum and polishes up nicley!
I stripped the transformer with strip-ez and repainted it. I see a lot of these restored and no one touches the power transformer.
Finally, after months of work, my preamp is about done.
It is a parafeed differential (push-pull) pre with a pair of 12A4's per side. The input transformers are Cinemag, the outputs are Magnequest 15K B7's.
It is a parafeed differential (push-pull) pre with a pair of 12A4's per side. The input transformers are Cinemag, the outputs are Magnequest 15K B7's.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi all !
so longtime Im have new Preampli :
its so all my idea about preampli tube , the soud verry good , it use OPT input, output with 4 capacitor Jensen, reguar with choke 25Hx2, 6C19P, and 12AZX7, OC3, phono with Ecc82 Telefunken, line with 4 Ecc88, ..v.v..! Some one as me use with OPT output, but Im have one pair NP 126 Tango, and one pair UTC30, use for 5K:600, and 10K: 600, so Im dont want to use them because with me OPT have broplem with Frequency, and not so good for my classic music
so longtime Im have new Preampli :
its so all my idea about preampli tube , the soud verry good , it use OPT input, output with 4 capacitor Jensen, reguar with choke 25Hx2, 6C19P, and 12AZX7, OC3, phono with Ecc82 Telefunken, line with 4 Ecc88, ..v.v..! Some one as me use with OPT output, but Im have one pair NP 126 Tango, and one pair UTC30, use for 5K:600, and 10K: 600, so Im dont want to use them because with me OPT have broplem with Frequency, and not so good for my classic music
