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In Reply to: What DaveInVA said... posted by Lew on August 4, 2006 at 08:39:09:
Awesome DaveInVA & Lew , Thats fantastic advice , I have a spare tube , so I will exchange this Hot Puppy out . All the rest are much cooler indeed . I ordered 10 new Sovtek 6as7-g's for the second amp .. + while I was testing the first amp , I managed to flash over 1/2 of one tube in the first few minutes . Sadly this was caused because of a faulty tube in V3 or V4 - the arcing happened in the 6sn7 and then was followed by a huge flash in a 6as7g & a simultaneous bang in the speaker that made me nearly 20 years older / or younger ..im not sure which ! . Problems are all fixed now ...bias & balance is settled nicely . I pre cured the tubes as per recommendations . The damaged / stress placed on the output tubes was my mistake - I used some used ex radio spares 6sn7's ....but now have all new Electroharmonix . Overall - ive learnt alot already ...and building a left hand / right hand amp to my own physical design has been a real challenge . This week I hope to complete the 2nd amp ...then all I need is a site to host the pics. Cheers guys for your advice . Much appreciated . Stu
Follow Ups:
have 5 ohm 5 watt resistors in the cathode circuits. *Nuch* more effective than the 1 ohm resistors of earlier units.
I'm sure you meant "much" not "nuch".
Anyway, what does that do to the output impedance? I assume you take the output off the plate with the resistor on the cathode side.
No, we take the output off the cathodes. The cathode resistors are in series with that. But when you total up the entire lot of them, the result is a negligable increase in output impedance. However the tubes work better together so the impedance goes back down a little. The result is lower distortion- meaning better low level detail and smoother sound. The tubes last longer too.
nt.
Oh man - ive just finished wiring in my 1 ohm resistors too ..along with the 150 ohms tonight ....looks like back to the soldering iron for me before before I go much further on the 2nd amp . I new things were going too smoothly
Stu
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