Bogen 8417 tube conversion..?

[Nichols]

Darren, thanks a million! This looks like the missing link... just have to put it all together (with a lot of help from the other members!). If you could post anything else you have relevant to this, i.e. your power supply diagram it would be very much appreciated. Thanks again! -N

[Turbo7MN]

Alright, I'll scan it when I have time tonight. Glad I could help.

[Nichols]

Hello all, has anyone had a chance to look at Darren's mod? This looks like something I can do... any comments or suggestions? I have a few questions but it doesn't look too difficult. Thanks.

[poobah]

Can you put it up here?

[Nichols]

It's post #70, just back a few. Here's the link to the drawing:
http://www.diyaudio.com/forums/attac...amp=1143156357

[John Rutha]

Hello everyone,

I to have aquired one of these amps. I am guessing that it is a class B amp because there is not much weight in the iron; I do know that it takes power to make power as I have built and modifyed a few of my own units. I am leaning in the direction of a total home brew with an ultra linear Mk3 output with 4 6L6GC, or EL34. At present my chasis is cathode biased as there is no C- supply, so I dont know if we all have the same Bogen M120.
Any way when I am working on an home brew output stage I always have a current meter, usually between cathodes and ground in the output circuit. Then if you know your plate voltage, and current you can calculate Ep * Ip = Plate dissipation in watts. So if there are (4) 8417 at 35 watts each total disipation cannot exceed 140 watts. A C- supply can easily be constructed to keep the proper negative charge on the grids.
My RCA Tube manual says a pair of 8417 in AB1 mode biases around - 15.5 volts if plate supply is 560 volts with an idle current of 100ma, plate dissipation would be 56 watts for the pair which is well below 35 + 35. and Signal power is 100 watts output. On the other hand (2) 6550 In AB1 require conciderably more negative bias for similiar operating conditions. It would be more like -31 volts on the grids with a plate supply of 600 volts idling at 105ma for a plate dissipation of 63 watts. and and an output of 100 watts. 6550 would need conciderably more -bias then 8417 in any operating condition, but it could be worked out. I don't much like the math. I just get in there with the meters and irons and do it. I have not yet smoked an amp. I know it is the stone age way of doing things but it works for me.
I sure would like to get a copy of the schematic because I have been out of work here in Pontiac Michigan for some time and am board as ----. Nichelous lives in Detroit. I live in Pontiac. May be me and him can make it a team effort. Well this is my first post. May be in a few I will be able to email you guys for the schematic and I will let you all know how it goes.

Happy Tubing Fellas

[Nichols]

Sorry man, take a look at the dates of the posts above.

Most of these guys were never of any real help, I gave up on the project and sold the amp long ago. I made more on the tubes than the amp itself. The schematic is long gone.

Sounds like sour grapes, huh? Too bad if any of you guys are offended.

[John Rutha]

Yes I didn't look at the post dates. As far as the schematic oh-well no big deal. I can pick one off the web for $10.00, but I probably dont need it. I think the only part of the amp I will save is the power transformer, and then only if it has any real horse power.

Thanks for the reply though.