Hi there
I’ve recently discovered this earlier amp (rm-10) which was in production until a few years ago.
I fell in love with simple el84 push-pulls years ago and my recent acquisition of a cr development Kalypso has comforted me in this direction.
RM-10 amps are barely available second hand and if they are, it’s from 110v countries and it would need a mod of the power transformer.
I wanted to study the schematic to see if that’s something for me.
If anyone has picked up / drawn the schematic from his/her amp or has it in the original service manual, and would be willing to share it, I’d be immensely grateful. By pm preferably as I guess there are enough commercial/ industrial copycats out there.
I’ve recently discovered this earlier amp (rm-10) which was in production until a few years ago.
I fell in love with simple el84 push-pulls years ago and my recent acquisition of a cr development Kalypso has comforted me in this direction.
RM-10 amps are barely available second hand and if they are, it’s from 110v countries and it would need a mod of the power transformer.
I wanted to study the schematic to see if that’s something for me.
If anyone has picked up / drawn the schematic from his/her amp or has it in the original service manual, and would be willing to share it, I’d be immensely grateful. By pm preferably as I guess there are enough commercial/ industrial copycats out there.
Yes and no. Plate voltage is reportedly 700v, achieved through a Latour rectifying doubler. The general building was documented in a test by 6moons
https://6moons.com/audioreviews/musicreference/rm10.html
From open sources I found this evening a partial schematic by a guy who serviced a faulty amp for a customer. https://m.xuite.net/blog/look_t/twblog/557138559
Some information is still missing and the schematic he did shows also some mods he performed. Somewhat confusing for an amateur like me.
https://6moons.com/audioreviews/musicreference/rm10.html
From open sources I found this evening a partial schematic by a guy who serviced a faulty amp for a customer. https://m.xuite.net/blog/look_t/twblog/557138559
Some information is still missing and the schematic he did shows also some mods he performed. Somewhat confusing for an amateur like me.
Personally, I wouldn't touch one with a 10 foot pole. Lots of good PP EL84 amp designs floating around this forum.
jeff
jeff
The person who tried to reverse engineer the RM-10 got a lot wrong, and yes he did remove the voltage doubler which I'll assume means reduced power so why bother. The challenge for Roger was to develop his own application for the EL-84 and not slave himself to the many applications available in the tube manuals which resulted in cricuits that delivered roughly half the power he achieved. Also, the guy reverse engineered a MkI version of the amp, the circuit and transformers being different from that of the more popular MkII version. Roger being Roger there are actually three different versions of the MkII. His philosophy being that as the designer he could change the circuit anytime he wanted and not rebadge the amp in the process. So if you can find a schematic, it most likely will be a MkI, and if it is one of the MkII circuits you might be able to figure it out only to be surprised it wasn't what you expected. Good luck with the transformers too. Some great minds I know tried to reverse engineer them without success.
Somewhere, here i believe, maybe AudioCircle, Modjeski described how he squeezed 40w out of pir of EL84s. Involve very high rails and special OPTs.
A well rrspected amplifier, one i would like to hear someday.
dave
A well rrspected amplifier, one i would like to hear someday.
dave
Makes no sense to me. You can get 40w or more out of a pair of sweep tubes no problem, and you don't need 700v rails to do it. Why torture a pair of 6BQ5s?
jeff
jeff
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The way he explains it they are not working that hard. Over my head.
dave
dave
Bias is 300 mv at which point current is 30 mA, and here it is, tube dissipation is 10 watts each so they are running well within their limits, no torturing. Plates show no sign of red plating at 300 mV and you can go as high as 400 mV if you want to on the bias. Bear in mind that while 700V is on the plates, now get ready here it is again, only 350V is on the screen.
I found this in a 6moons review of this amp. "At the recommended bias current of 30mA/pair, the idling dissipation is nine watts or 75% of the tubes' rating."
jeff
Roger estimated tube life to be 5,000 - 10,000 hours if the amp is played below clipping at the recommended bias setting. I think that is pretty reasonable. I finally had to change tubes in mine after 10 years of consistent use. In addition, only drew 70 watts at idle vs. 220 watts for the Dynaco ST-35 which put out about 18 watts per channel.
The design philosophy of the amplifier is spelled out in its manual. If one is really interested in learning some of the details I would recommend acquiring one.
The design philosophy of the amplifier is spelled out in its manual. If one is really interested in learning some of the details I would recommend acquiring one.
I’ve offered to the successor company to pay for the manual (possibly containing the schematic) and possibly the transformers, which were also sold as as special package at some stage. But not anymore.
Thanks to all for your comments. I did not mean to launch a debate on the merits of the circuit, which was already commented here and there. Just trying to get a reliable schematic to decide whether I want to build an amp for myself or not, as getting a used amp is difficult and I would anyway need to convert it to 230v.
Thanks to all for your comments. I did not mean to launch a debate on the merits of the circuit, which was already commented here and there. Just trying to get a reliable schematic to decide whether I want to build an amp for myself or not, as getting a used amp is difficult and I would anyway need to convert it to 230v.
Converting it to 230v is no problem, buy a 110v one, keep it stock and buy a step down transformer or what i personally do is buy a big used PA amp transformer with secondary which give me between 110v and 120v (the last in 1000VA cost me 40€) and serves me for all my devices in 110/120V.
Thank you for introducing me to this oddity.
Thank you for introducing me to this oddity.
At some stage, Roger (owner of Music Reference) offered against a financial contribution, the schematic and manual providing explanations of the circuit, against also the promise of the buyer not to make it public. I’m happy to give a compensation to someone who would send me a scan/copy, under similar terms.
Alternatively, I’m interested in a similar reliable schematic that allows to run the el84 at a high voltage / low current bias, and which has been successfully tested.
