What do you want to do with it? Leave it as is or build something with the tubes and PS?
There has been some discusions on the el84 SE designs (http://www.diyaudio.com/forums/showthread.php?s=&threadid=47048
that might help.
I recently stripped a similar chassis and built a el84 from a design found in the above thread.
rick
There has been some discusions on the el84 SE designs (http://www.diyaudio.com/forums/showthread.php?s=&threadid=47048
that might help.
I recently stripped a similar chassis and built a el84 from a design found in the above thread.
rick
this is somewhat the idea i have for rebuilding it. i have some left over aluminum stock left over from the chipamps i was working on.
wood on the front and back with one inch wood overhang on the sides and rounded off. its not the right iron but it gives me a idea
of the space needed for the right one.
i allso replaced the caps and was really suprized on how nice it sound. single ended sounds great.
wood on the front and back with one inch wood overhang on the sides and rounded off. its not the right iron but it gives me a idea
of the space needed for the right one.
i allso replaced the caps and was really suprized on how nice it sound. single ended sounds great.
Attachments
power resisters
something like this? i could just install them on the heatzinc on the under side. in series
http://www.riedon.com/ual.htm
something like this? i could just install them on the heatzinc on the under side. in series
http://www.riedon.com/ual.htm
> would a single ended tube amp make a good headphone amp?
Fix what's broke: it should be fine about the way it is.
5 Watts into 4Ω is 4.5V RMS. 4.5V RMS onto 32Ω is 0.6W; on 300Ω is 70mW, perfectly acceptable headphone power. Running lightly loaded like that the THD will be low and mostly even-order.
Just to keep the OPTs from arcing, I'd put about 10Ω 10W on the secondary permanently. And to reduce accidents with 0.6W into 32Ω I might put 22Ω between the secondary and the headphone jack.
It already has volume, balance, bass, treble controls. Funky old passive tone controls, I'm sure, but they were always pleasant. The 12AX7 is plenty to recover the loss in the tone controls and bring it up to 6BQ5 grid level.
I really would not change a thing, except all those caps look old and decrepit to me and I'd probably replace them all without much testing. Even if they measured good now, a few hours of voltage might be the last straw. I'd double the uFd of the audio caps (replace 0.01uFd with 0.02uFd), and at least quadruple the power supply caps (100uFd in place of 20uFd). Headphones might need even more smoothing: consoles like this only reduced hum enough so you would not hear it a few feet away; with headphones you have to go much cleaner. It might even suggest adding another R-C section to the power chain (L-C if you have the iron or cash).
The other way to go is lose the tone controls and apply negative feedback. For a speaker amp, I'd be real tempted. For a headphone amp, the only strong reason to add NFB is to extend the bandwidth of the output transformer, which may be no better than the 8-inch speakers it originally drove.
Did you actually pay $50 for this hunk of junk? {sigh} I can't remember how many of those I've thrown away over the decades. It probably cost less than that new; or rather, $100 bought this amp, a couple 8" speakers with 3" tweeters, a turntable, and a "Mediterranean Walnut Furniture-Grade" cabinet. My father still has one, Big-Name-Brand (RCA), up in the garage. If the birds and bats have not nested in it, maybe he should eBay it.
Fix what's broke: it should be fine about the way it is.
5 Watts into 4Ω is 4.5V RMS. 4.5V RMS onto 32Ω is 0.6W; on 300Ω is 70mW, perfectly acceptable headphone power. Running lightly loaded like that the THD will be low and mostly even-order.
Just to keep the OPTs from arcing, I'd put about 10Ω 10W on the secondary permanently. And to reduce accidents with 0.6W into 32Ω I might put 22Ω between the secondary and the headphone jack.
It already has volume, balance, bass, treble controls. Funky old passive tone controls, I'm sure, but they were always pleasant. The 12AX7 is plenty to recover the loss in the tone controls and bring it up to 6BQ5 grid level.
I really would not change a thing, except all those caps look old and decrepit to me and I'd probably replace them all without much testing. Even if they measured good now, a few hours of voltage might be the last straw. I'd double the uFd of the audio caps (replace 0.01uFd with 0.02uFd), and at least quadruple the power supply caps (100uFd in place of 20uFd). Headphones might need even more smoothing: consoles like this only reduced hum enough so you would not hear it a few feet away; with headphones you have to go much cleaner. It might even suggest adding another R-C section to the power chain (L-C if you have the iron or cash).
The other way to go is lose the tone controls and apply negative feedback. For a speaker amp, I'd be real tempted. For a headphone amp, the only strong reason to add NFB is to extend the bandwidth of the output transformer, which may be no better than the 8-inch speakers it originally drove.
Did you actually pay $50 for this hunk of junk? {sigh} I can't remember how many of those I've thrown away over the decades. It probably cost less than that new; or rather, $100 bought this amp, a couple 8" speakers with 3" tweeters, a turntable, and a "Mediterranean Walnut Furniture-Grade" cabinet. My father still has one, Big-Name-Brand (RCA), up in the garage. If the birds and bats have not nested in it, maybe he should eBay it.
most of the caps have been replaced. it was about $50 on ebay plus the shiping. basically i paid for the iron its the only thing thats going to be original if you have any amps like this i would post it on ebay thay sell.
i got rid of all the pots. i have a old alps pot somwarez around here ill use that.
i like rebuilding bogen amps this one is a side project
ill try
Just to keep the OPTs from arcing, I'd put about 10Ù 10W on the secondary permanently. And to reduce accidents with 0.6W into 32Ù I might put 22Ù between the secondary and the headphone jack.
and see how it turns out.
if you have any amps like this i would post it on ebay thay sell.i got rid of all the pots. i have a old alps pot somwarez around here ill use that.
i like rebuilding bogen amps this one is a side project
ill try
Just to keep the OPTs from arcing, I'd put about 10Ù 10W on the secondary permanently. And to reduce accidents with 0.6W into 32Ù I might put 22Ù between the secondary and the headphone jack.
and see how it turns out.
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