Porkchop, slightly OT, but... I'd highly recommend getting a copy of "Similarities in Physics," by Shive and Weber. Despite the rather dry title, it's very readable and enjoyable. The focus of that book is showing that the same equations pop up in differing contexts (e.g., mechanics and electronics), and that there's a sound basis in drawing these analogies.
B+ 4v over schematic value acceptable?
I almost finished this preamp last weekend, and the B+ was within 2 volts of the predicted value! That PSU Designer II software is awesome!
I thought I'd ask this question even though it probably doesn't mean anything. Is running the 6SN7GT's at 254V ok even though the schematic says 250V? This could be due to high power line voltage right? Regardless, I don't think this is a big deal right?
Joel?
Glenn
I almost finished this preamp last weekend, and the B+ was within 2 volts of the predicted value! That PSU Designer II software is awesome!
I thought I'd ask this question even though it probably doesn't mean anything. Is running the 6SN7GT's at 254V ok even though the schematic says 250V? This could be due to high power line voltage right? Regardless, I don't think this is a big deal right?
Joel?
Glenn
10% either way on ANY voltage in any tube amp is acceptable. And I'm told that in the old, pre-DMM days, a 20% margin was the limit.
Some old power amp manuals don't even give readings for the small signal tube voltages because they would've had hundreds of guys calling in wondering if their unit was broken because it was a few volts off here and there.
Joel
Some old power amp manuals don't even give readings for the small signal tube voltages because they would've had hundreds of guys calling in wondering if their unit was broken because it was a few volts off here and there.
Joel
It lives!
ALL RIGHT!!
Just fired it up, and NO SMOKE! It actually works.
I'm not sure that this is a fair test as it's hooked to an integrated amp and not just a power amp. I almost forgot how fun it is to thread an open reel tape deck, not to mention the sound!
Please excuse the messy workbench
http://webpages.charter.net/porkchop/tube_stuff/front.jpg
http://webpages.charter.net/porkchop/tube_stuff/side.jpg
http://webpages.charter.net/porkchop/tube_stuff/with_friends.jpg
ALL RIGHT!!
Just fired it up, and NO SMOKE! It actually works.
I'm not sure that this is a fair test as it's hooked to an integrated amp and not just a power amp. I almost forgot how fun it is to thread an open reel tape deck, not to mention the sound!
Please excuse the messy workbench
http://webpages.charter.net/porkchop/tube_stuff/front.jpg
http://webpages.charter.net/porkchop/tube_stuff/side.jpg
http://webpages.charter.net/porkchop/tube_stuff/with_friends.jpg
SY said:
Yes, you can't clean and build at the same time.
No, Its' a cheap Sony but it works pretty well. I have two as they were both saved from the dumpster in '78.
I'm not too crazy about the sound of the Chinese 6SN7GT tubes, so I'll probably order a few different brands. Any recommendations on favorite brands of this tube?
Thanks
Glenn
I'm probably the wrong person to ask about currently-available 6SN7s- I've been living off my stock of 5692s purchased long before these were considered audio jewelry. Morgan Jones recommends Pinnacle 6J5GT (single triode version of 6SN7), and seems quite keen on 6SN7 variants with carbonized envelopes.
Re: "Joel was kind enough to send me this suggestion also..."
Okay Joel-
Now I think I'd like to try a bench test with a transformer for driving headphones now that I have the preamp working. Does a 1.5k primary with around 100 ohms secondary sound useable? Or do I have to match the secondary exactly with my 130 ohm headphones?
I assume this is not a large transformer. Any ideas where to buy one of these? Do I look for "impedance matching" transformer types, or "interstage"?
Thanks
Glenn
Joel said:
Okay Joel-
Now I think I'd like to try a bench test with a transformer for driving headphones now that I have the preamp working. Does a 1.5k primary with around 100 ohms secondary sound useable? Or do I have to match the secondary exactly with my 130 ohm headphones?
I assume this is not a large transformer. Any ideas where to buy one of these? Do I look for "impedance matching" transformer types, or "interstage"?
Thanks
Glenn
Sorry to be a contrarian, but I don't like the idea of using a typical "matching transformer", or using capacitor coupling to it (parafeed).
With an 8k impedance driver like a plate-loaded 6SN7, I would simply use an off-the-shelf 6k-10k primary output transformer, and hook the headphones up to the 16 ohm tap. You could do push-pull, but an SE unit would also be fine at the microwatt levels needed.
There was an excellent thread here discussing just such a design, with good informative posts by PRR. Search for it.
Joel
With an 8k impedance driver like a plate-loaded 6SN7, I would simply use an off-the-shelf 6k-10k primary output transformer, and hook the headphones up to the 16 ohm tap. You could do push-pull, but an SE unit would also be fine at the microwatt levels needed.
There was an excellent thread here discussing just such a design, with good informative posts by PRR. Search for it.
Joel
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