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My Winter Project

GordonW said:
Micah, that amp doesn't have a power supply choke, does it?
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Nope, I wish I had room for one, but this thing is crammed.

GordonW said:
Was wondering... as I'm thinking of building up my AP60s here (that I got from Tinkerbelle), with plate-plate feedback, like you were attempting to use earlier in the thread. I have a good pair of 300ma chokes... and there's room to put them on top of the chassis, one in each amp. That might get rid of enough power supply noise, to make plate-plate feedback plausible, no?
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Chokes should definitely help if you're using pretty sensitive speakers. Even with the power-supply rejection that PP has, some hum can still get through by unmatched tubes, etc. IIRC there is about 1.5mVrms of hum on the output of this amp. Most of that is due to the power supply ripple at the output tubes. I ended up setting on feedback from the 70VCT windings as feedback to the driver stage, it seems to work pretty well. I also debated connecting the screens through the winding, but I think I've gotta stop somewhere...:D


GordonW said:
Mine will be interesting- I, too am dealing with 600+ volts of B+... I'm thinking of using 6146 tubes, ala early model Ampegs and the original Acrosound Ultralinear amp. There's actually tertiary windings (approximately 25%) that would allow me to use these tubes in ultralinear, apparently... as I posted in my other thread about this...
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I thought about using those tube early on, but the thought of replacing an octet didn't fair well with my wallet :D
 
GordonW said:
Mine will be interesting- I, too am dealing with 600+ volts of B+... I'm thinking of using 6146 tubes, ala early model Ampegs and the original Acrosound Ultralinear amp. There's actually tertiary windings (approximately 25%) that would allow me to use these tubes in ultralinear, apparently... as I posted in my other thread about this...
Click to expand...

Ya know Gordon, you can also shove that tertiary in the cathode circuit instead, and just fix the screen voltage. That way you get UL feedback to the screen via the cathode modulation, and standard negative feedback to the grid via for better damping, Quad II style. Sweeet. :scratch2:
 
Having stumbled across this thread again it came to my mind that I ought to complete it by posting the final schematic for this amp that Micah supplied to me when I purchased it from him as he made a few changes since then. It's a little tough to read because AK shrinks it down but if you want the full-size high res version, just PM me and I'd be glad to provide.

I have at least a few hundred hours on this amp since I acquired it without a hiccup :thmbsp: Cranking out some classical music right now from a Fisher KM-60 tuner :music:

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Hi,

A) very nice thread! I acquired one of these the other day. Bogen has always (In my opinion) been very honest about his freq response claims. I've built using his iron a few other times with very good measured results!

B) I like what you have done! A few questions though. The final schematic posted does not contain the CCS on the driver stage. Did you remove it? Why the Pentode on the CA stage?

Sorry to bring this back to life. Just curious about your adventure. I'm doing similar, but transplanting the whole thing to another custom chassis. I'm adding a SG supply as well as individual bias.

Thanks!

Blair
 
Blair_4 said:
Hi,

A) very nice thread! I acquired one of these the other day. Bogen has always (In my opinion) been very honest about his freq response claims. I've built using his iron a few other times with very good measured results!

B) I like what you have done! A few questions though. The final schematic posted does not contain the CCS on the driver stage. Did you remove it? Why the Pentode on the CA stage?

Sorry to bring this back to life. Just curious about your adventure. I'm doing similar, but transplanting the whole thing to another custom chassis. I'm adding a SG supply as well as individual bias.

Thanks!

Blair
Click to expand...

Ditto on what Blair asked. I am currently working on a set of MO100a's.

TIA!
Mark
 
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Blair_4 said:
Hi,

A) very nice thread! I acquired one of these the other day. Bogen has always (In my opinion) been very honest about his freq response claims. I've built using his iron a few other times with very good measured results!

B) I like what you have done! A few questions though. The final schematic posted does not contain the CCS on the driver stage. Did you remove it? Why the Pentode on the CA stage?

Sorry to bring this back to life. Just curious about your adventure. I'm doing similar, but transplanting the whole thing to another custom chassis. I'm adding a SG supply as well as individual bias.

Thanks!

Blair
Click to expand...

I'm not sure the KT77s had some problems (not out of the question with JJs) or there was some stability issues, but I changed up the driver stage to something a little simpler for longevity. No solid state means it will be easier to work on should something bad happen.
 
bricktop said:
I'm not sure the KT77s had some problems (not out of the question with JJs) or there was some stability issues, but I changed up the driver stage to something a little simpler for longevity. No solid state means it will be easier to work on should something bad happen.
Click to expand...

Good point and thanks for the update!
BTW - awesome build you did there.:thmbsp:

Mark
 
I built a pair of PP 1625 monos with 12SN7s 30 years ago. I went with used EF Johnson for the ceramic parts. The outputs were Acrosound TO-300s, and the power supply iron salvaged too. I used Acrosound's catalog schematic for a road map. Tubes and resistors were the only new parts. Man, when you can get 1945 milspec NIB NOS versions of a 6L6 glassware for pocket change, AND the tubes work so nicely with the music making, heck....Life is Good!!! This is an ancient post I'm responding to, but I'm ancient too. ;)
 
bricktop said:
Converting a Bogen MO-200A into something useful...

I got a beat-up bogen a while ago for $60 from a friend (which he got from Douglas). Finally got around to rebuilding it. I know there are a bunch of these things around, so I'm posting my refurb here for anyone that wants to a refurb on theirs, or just people who like tube eye candy :D. I'm just posting now because I hope to get it up and running soon. Sometimes they pop up on that auction site here and there.

Amp specs:
plate voltage: 680 VDC
Screen voltage: 340 VDC
Power tubes: originally 8x 8417, converted to 8x JJ E34L
class: little AB, mostly B
power output: transformers are good for 100W each 20Hz-50KHz from what I gather here: http://www.montagar.com/~patj/bogenspecs.htm, but I'll see what it actually does soon.
drivers: originally two 7247s, now 4x 6CL6 LTP w/CCS

I took some pics here of the chassis and fit-testing the caps. I like how they go in here, pretty proud-a that:D since you can't see the clamps from the top. I'm gonna go with the blumlien cathode bias scheme so there will be no bias potentiometers to adjust. thanks for the suggestion Douglas.:thmbsp:

The little spots of gray on the chassis is JB weld that I used to fill in the old holes...seems to work well and paint goes over it nicely. Anyways, Happy Holidays everyone. This will probly be one of last posts before Christmas b/c I'll be going home where there is only dial-up, and that connection just makes me mad so I don't use it:sigh:
bye yall':music:
Click to expand...
lookin good, buddy!
 
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