Yes, this would be strictly for guitar. A lot of guys are after distortion so would probably be more interested in a preamp that they can overdrive, I'm more interested in clean. If I want some overdrive I'll use a pedal. I did some reading and not only do the 6550's fit the sockets, there are some brands of this tube that are highly recommended for guitar amps. I thinks the KT88 is similar, but now I'm already out of my league...
I have a Bogen M60A that's identical to this one except it only uses a pair of 8417s, that thing is a wicked guitar amp. I start to get breakup around halfway up, so I'd imagine you'd have planty of clean headroom with this amp.
A guy on Ampage helped me draw up a bias voltage doubler/ajustment circuit that would allow 6550s or KT88s to be used. I haven't done it yet, but it's identical to the circuit he runs on his 8417-powered Bogen.
http://www.diyaudio.com/forums/attachment.php?s=&postid=876588&stamp=1143156357
Sorry it's kinda sloppy. The 22k resistors at the end are in the existing circuit. I have a schematic of the full redesigned power supply I can post if you want it.
Fun fact: There's no amplification stage between the inputs and master volume. I keep the input volume all the way up and only adjust the master since they both more or less do the same thing. I plan on moving it later in the circuit one of these days, this would probably help with clean headroom too.
6EU7s are awesome tubes by the way, don't convert them to anything else! I've found 6EU7s to be really cheap compared to 12AX7s. I got both an RCA and a Mullard a while back for less than $20 on ebay. The Mullard turned out to be a tad bit microphonic, but whatever. I see NOS pairs of 6EU7s (mostly Mullards) go for well under $50 every day.
Let me know what you end up doing with it.
-Darren
A guy on Ampage helped me draw up a bias voltage doubler/ajustment circuit that would allow 6550s or KT88s to be used. I haven't done it yet, but it's identical to the circuit he runs on his 8417-powered Bogen.
http://www.diyaudio.com/forums/attachment.php?s=&postid=876588&stamp=1143156357
Sorry it's kinda sloppy. The 22k resistors at the end are in the existing circuit. I have a schematic of the full redesigned power supply I can post if you want it.
Fun fact: There's no amplification stage between the inputs and master volume. I keep the input volume all the way up and only adjust the master since they both more or less do the same thing. I plan on moving it later in the circuit one of these days, this would probably help with clean headroom too.
6EU7s are awesome tubes by the way, don't convert them to anything else! I've found 6EU7s to be really cheap compared to 12AX7s. I got both an RCA and a Mullard a while back for less than $20 on ebay. The Mullard turned out to be a tad bit microphonic, but whatever. I see NOS pairs of 6EU7s (mostly Mullards) go for well under $50 every day.
Let me know what you end up doing with it.
-Darren
Allright!
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
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
It's post #70, just back a few. Here's the link to the drawing:
http://www.diyaudio.com/forums/attachment.php?s=&postid=876588&stamp=1143156357
http://www.diyaudio.com/forums/attachment.php?s=&postid=876588&stamp=1143156357
Bogen M120
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
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
Way too late
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.
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.
Bogen M 120
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.
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.
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