Ok, so what you need to do is this. Look at the bottom of the amplifier and write down the values of the resistors.
We are most interested in the 3 tube sockets at the front of the amp, then the 4 that are behind...
There are 9 pins on each tube socket. they are numbered in the clockwise direction from below, starting at 1 after the gap. There will be a gap... It goes 1, 2, 3, 4, etc... to 9. Read the resistor values for each green resistor and post them here please.
The resitors are the little green guys. Most resistors have little strips of color on them to indicate their value. The ones in this amp are (metal film I believe) and have actual numbers printed on them.
Please get those numbers and post them here with the pin they are attached to for each tube socket.
We are most interested in the 3 tube sockets at the front of the amp, then the 4 that are behind...
There are 9 pins on each tube socket. they are numbered in the clockwise direction from below, starting at 1 after the gap. There will be a gap... It goes 1, 2, 3, 4, etc... to 9. Read the resistor values for each green resistor and post them here please.
The resitors are the little green guys. Most resistors have little strips of color on them to indicate their value. The ones in this amp are (metal film I believe) and have actual numbers printed on them.
Please get those numbers and post them here with the pin they are attached to for each tube socket.
Here are some schematics I found through google that kind of make more sense:
http://susumu-oiso.homelinux.com/download/other/RFFlow-6RA8_AMP.pdf
http://tonys.cocolog-nifty.com/photos/uncategorized/2012/03/20/img_0012.jpg
6RA8
There are more... many possibilities exist. The last one has a voltage doubler so I am thinking it might be close. Some of these schematics have real potential.
Yahoo.jp is a good source for electronics parts within Japan. Pity it is so prohibative to purchase as a foreigner....
http://susumu-oiso.homelinux.com/download/other/RFFlow-6RA8_AMP.pdf
http://tonys.cocolog-nifty.com/photos/uncategorized/2012/03/20/img_0012.jpg
6RA8
There are more... many possibilities exist. The last one has a voltage doubler so I am thinking it might be close. Some of these schematics have real potential.
Yahoo.jp is a good source for electronics parts within Japan. Pity it is so prohibative to purchase as a foreigner....
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http://www.asahi-net.or.jp/~up2j-knst/tube/6ra8pp-3.jpg
Different configuration but the same basic parts. The output transformers in this example shown appear to be 4 ohm. I think it would be the right thing to do to hunt down the 6RA8 and give it a try (with Variac). What would be the other tubes I should muster?
Different configuration but the same basic parts. The output transformers in this example shown appear to be 4 ohm. I think it would be the right thing to do to hunt down the 6RA8 and give it a try (with Variac). What would be the other tubes I should muster?
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Same transformers unfortunately does not help much. If you happen to have the schematic then ok, post it. BUT: Please read off the resistor values and associated pins they are attached to. This will help a LOT. Then we can easily make progress by ruling out tubes....
The first socket, right to left. pin #1 has a 30. #2-#7 have a .957 resistor. #6 has a 30. #8 has a 30.
2nd socket has none.
3rd socket #1 has 30. #2-#7 have 1.0. #6 has a 30
2nd socket has none.
3rd socket #1 has 30. #2-#7 have 1.0. #6 has a 30
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I guess it is an amateur made a 6R-A8 pp stereo amp.
The circuit may be copied of the LUX, Transformer Kit-KMQ8, which has 7 tubes.
Hiro
Tubologic, I think, already correctly identified the amp, did you try to match up the part values?
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From here:
From here:
There will be some wires attached to the pins which lead to the board in the middle. The resistors will be on that board. Also see if any pins are connected together with a wire.
Try to see which pins lead to which resistor for the 2nd socket. Some resistors might have a "K" or an "M" after the number - that is important.
The A2500 schematic is looking likely...
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Early to mid 1960s vintage based on the resistors and coupling caps used, and I'd wager it's not a kit.
Appears to use fixed bias output stage which is adjusted by the two pots to left located above 3 electrolytics.
Being Lux iron the quality is going to be pretty good, but this thing needs a full restoration job - most of the parts are going to need to be replaced I think based on my experience with Japanese amps of that era.
I'd pass it along to someone who can restore it or alternately have said person fix it for you.
Appears to use fixed bias output stage which is adjusted by the two pots to left located above 3 electrolytics.
Being Lux iron the quality is going to be pretty good, but this thing needs a full restoration job - most of the parts are going to need to be replaced I think based on my experience with Japanese amps of that era.
I'd pass it along to someone who can restore it or alternately have said person fix it for you.
Thanks for taking the time to study and talk about this curiosity. I'm seriously impressed with the knowledge you all have and the kind willingness to share that knowledge. RESPECT!
Ok, its not tidy built but looks like a kit is what I meant. full wave voltage doubler? ugh.Probably best to strip it for parts.
tell that to Patrick Turner.....powersupplies
Properly designed voltage doublers work just fine in my experience. Cap quality is important..
The Citation II and a number of other extremely well regarded amplifiers had doublers..
The Citation II and a number of other extremely well regarded amplifiers had doublers..
FWIW, i stopped using full wave center tapped traffos and rectifiers a long time ago and will never go back...
I guess we are never too old to learn something old new again! I did some simulations and I like a lot of what I saw. Its about as fast as what I recently do with damper diodes, but with much less ripple. Nicely inexpensive too. Important not to use too high capacitance though...
What's a good approach for soft start? I'm definitely going to try this again... 40uF stacked motor run caps seem to work very nice in simulation.
Ian
Hi Ian,
You'll need to experiment to find what is best for your application, in general larger caps improve voltage regulation under varying load. Motor runs are a good choice both for their generally high ripple current rating and low ESR..
Best place to put inrush suppression is probably on the primary; there are a variety of choices depending on desired level of complexity (or the reverse) - at the simplest an NTC varistor can work well, but I like to bypass them (with a timed relay or similar) once they have done their job - they last longer that way and there is no question about what they might or might not be doing in terms of degrading supply performance since they are out of circuit. (This way they are ready to go in the event of a transient or other mishap.)
You'll need to experiment to find what is best for your application, in general larger caps improve voltage regulation under varying load. Motor runs are a good choice both for their generally high ripple current rating and low ESR..
Best place to put inrush suppression is probably on the primary; there are a variety of choices depending on desired level of complexity (or the reverse) - at the simplest an NTC varistor can work well, but I like to bypass them (with a timed relay or similar) once they have done their job - they last longer that way and there is no question about what they might or might not be doing in terms of degrading supply performance since they are out of circuit. (This way they are ready to go in the event of a transient or other mishap.)
another plus to this is the lower voltage involved relaxes insulation requirements a bit.....
goodbye to 800 volt windings, we do not need them anymore...plus they can run cooler
and with better transformer utilization than full wave center tapped traffos...
i think Edcor and Hammond should now make traffo offerings based on the full wave voltage doublers...
they will be cheaper to make too and so can cost less...
Where do you put inrush current limiting? It depends. 😉 In an amp with an O/P tube bias supply, put the NTC devices on the rectifier winding. The very last thing you want is a delay in the rise of the C- rail. 
Big 'lytics in a doubler stack crush the ripple fundamental and improve regulation, but introduce ripple overtones into the rail. Look at superior implementations of doubler PSUs, like those found in the H/K Cit. 2 and Marantz 8B, and you'll see a choke between the cap. stack and the reservoir capacitor. The choke is more important for attenuating ripple overtones than it is for attenuating the ripple fundamental. A refinement to the "Deuce" and "8B" setups is to install a "hash" filter LC section made from a high current RF choke and a 1000 pF. mica or NPO ceramic cap. between the doubler stack and the main filter choke. The "hash" filter keeps crud from sneaking into the B+ rail via the winding capacitance of the main choke. The technique described works any time HIGH valued cap. I/P filters are employed, not just doubler setups.
Big 'lytics in a doubler stack crush the ripple fundamental and improve regulation, but introduce ripple overtones into the rail. Look at superior implementations of doubler PSUs, like those found in the H/K Cit. 2 and Marantz 8B, and you'll see a choke between the cap. stack and the reservoir capacitor. The choke is more important for attenuating ripple overtones than it is for attenuating the ripple fundamental. A refinement to the "Deuce" and "8B" setups is to install a "hash" filter LC section made from a high current RF choke and a 1000 pF. mica or NPO ceramic cap. between the doubler stack and the main filter choke. The "hash" filter keeps crud from sneaking into the B+ rail via the winding capacitance of the main choke. The technique described works any time HIGH valued cap. I/P filters are employed, not just doubler setups.
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