I took the advice and corresponded with Jim McShane. After explaining the circumstances (he also used the term Cheap Charlie) he offered me a deal on what he called a "cool biased" quad of Sovteks. Tube selection by himself personally.
He feels those would likely be the most suitable given the unit they are going into and that it would remain a "Cheap Charlie".
The day after tomorrow I'll be getting what capacitors I can get locally. With any luck I'll have them installed by Saturday. The tubes from Jim, I could have as soon as the next weekend.
I'm not expecting much if any change once the capacitors are in, using the tubes I have on hand, but......?
When the new tubes arrive I sure hope red plating and accompanying distortion are problems solved. I also hope that "cool biased" means they won't be throwing off as much heat as the present set does.
This experience has me thinking mainstream Japanese receivers from the 1960's are nothing to go out of one's way for. The attractant for me was it reminded me of one I bought used while still in high school. That one was branded Chrysler but I'm sure was a bit older than this one I just acquired. Although they share similar "lines" the Chrysler had no magnetic phono input, had a "Magic Eye" tube, no FM stereo but SW and dual AM dial scales. I now believe it was a twin to another I saw branded Pioneer. That Chrysler worked well for me the couple of years I had it and at least a couple more for the neighbour kid I sold it to.
He feels those would likely be the most suitable given the unit they are going into and that it would remain a "Cheap Charlie".
The day after tomorrow I'll be getting what capacitors I can get locally. With any luck I'll have them installed by Saturday. The tubes from Jim, I could have as soon as the next weekend.
I'm not expecting much if any change once the capacitors are in, using the tubes I have on hand, but......?
When the new tubes arrive I sure hope red plating and accompanying distortion are problems solved. I also hope that "cool biased" means they won't be throwing off as much heat as the present set does.
This experience has me thinking mainstream Japanese receivers from the 1960's are nothing to go out of one's way for. The attractant for me was it reminded me of one I bought used while still in high school. That one was branded Chrysler but I'm sure was a bit older than this one I just acquired. Although they share similar "lines" the Chrysler had no magnetic phono input, had a "Magic Eye" tube, no FM stereo but SW and dual AM dial scales. I now believe it was a twin to another I saw branded Pioneer. That Chrysler worked well for me the couple of years I had it and at least a couple more for the neighbour kid I sold it to.
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Don't get overly "down" on the Japanese tubed receivers.
Sansui used Hashimoto O/P trafos, which are quite decent. I don't know about the unit in question.
Voltage doubler B+ supplies need not be bad. Some of the very best amps ever (H/K Cit. 2, Marantz 8B, & some "Mac" models) employ the topology.
As for "Cheap Charlie" DC heaters, many manufacturers used the technique. If nothing else, it's economical. I despise "Cheap Charlie" and repeatedly recommend construction of proper, regulated, 12 VDC heater supplies. I also advise separate RC bias networks in each channel.
IIRC, "cold" biasing means that for a given grid bias voltage value plate current will be comparatively low.
Sansui used Hashimoto O/P trafos, which are quite decent. I don't know about the unit in question.
Voltage doubler B+ supplies need not be bad. Some of the very best amps ever (H/K Cit. 2, Marantz 8B, & some "Mac" models) employ the topology.
As for "Cheap Charlie" DC heaters, many manufacturers used the technique. If nothing else, it's economical. I despise "Cheap Charlie" and repeatedly recommend construction of proper, regulated, 12 VDC heater supplies. I also advise separate RC bias networks in each channel.
IIRC, "cold" biasing means that for a given grid bias voltage value plate current will be comparatively low.
Well, the die's been cast and known good output tubes will be shipped tomorrow. I probably should not have purchased that full compliment of used tubes right off the bat but it made sense at the time. Hopefully the others (minus 6BQ5's) will pull their weight and not be problematic.
So far it's about $200 spent on tubes with an uncertain outcome. Reminds me somewhat of what days of heavy drinking were like.
Probably completely wrong but I'm imagining that cold biasing has the upside of operating under less than ideal conditions but a downside of fewer watts output.
How important are tube shields? Since this receiver was totally tubeless, the three tubes that had them don't anymore. Two went on 12AX7's and one was for a 6AQ8.
I fielded that question to Jim McShane thinking if they are somewhat mandatory and he happens to have spares, he could send some with the tubes
So far it's about $200 spent on tubes with an uncertain outcome. Reminds me somewhat of what days of heavy drinking were like.
Probably completely wrong but I'm imagining that cold biasing has the upside of operating under less than ideal conditions but a downside of fewer watts output.
How important are tube shields? Since this receiver was totally tubeless, the three tubes that had them don't anymore. Two went on 12AX7's and one was for a 6AQ8.
I fielded that question to Jim McShane thinking if they are somewhat mandatory and he happens to have spares, he could send some with the tubes
Some progress but not total
Since my last post, I have replaced every tubular film cap and those (probably also film) that were wax coated.
Some of the electrolytics had already been replaced. Or more accurately, there were some new electrolytics in place when I got the receiver. Those ones I left alone but replaced all other except two.
At this point, I am going to say 80% success. Red plating no longer occurs and the fidelity remains constant.
Before, after two minutes, fidelity degenerated into distortion and an intermittent (for lack of a better term) crackling sound occurred.
So now there is no distortion but that crackling sound persists, although to a lesser extent, and is confined to the left channel. Also, there is a "rushing" sound which was also there before but it too now seems to be confined to the left side.
By comparison, the right channel is nearly noise free.
These anomalies are unaffected by volume, bass, treble or input selection.
I may be totally wrong about this but my limited knowledge has me thinking the problem is in the power supply which is where the two old, original electrolytics are located.
The reason they have not been replaced is they are large and therefore expensive. My budget was hoping I could get away without changing them.
I can push on and replace those two, perhaps subbing 3 individual caps for the multi-section can which is one of them. For me it is a shot in the dark to see if that would work or not.
If that doesn't do the trick and I went beyond replacing film and electrolytic capacitors, would it be resistors I'd need to replace to eliminate the above described noisiness?
FWIW, the bottom cover and case are off.
Since my last post, I have replaced every tubular film cap and those (probably also film) that were wax coated.
Some of the electrolytics had already been replaced. Or more accurately, there were some new electrolytics in place when I got the receiver. Those ones I left alone but replaced all other except two.
At this point, I am going to say 80% success. Red plating no longer occurs and the fidelity remains constant.
Before, after two minutes, fidelity degenerated into distortion and an intermittent (for lack of a better term) crackling sound occurred.
So now there is no distortion but that crackling sound persists, although to a lesser extent, and is confined to the left channel. Also, there is a "rushing" sound which was also there before but it too now seems to be confined to the left side.
By comparison, the right channel is nearly noise free.
These anomalies are unaffected by volume, bass, treble or input selection.
I may be totally wrong about this but my limited knowledge has me thinking the problem is in the power supply which is where the two old, original electrolytics are located.
The reason they have not been replaced is they are large and therefore expensive. My budget was hoping I could get away without changing them.
I can push on and replace those two, perhaps subbing 3 individual caps for the multi-section can which is one of them. For me it is a shot in the dark to see if that would work or not.
If that doesn't do the trick and I went beyond replacing film and electrolytic capacitors, would it be resistors I'd need to replace to eliminate the above described noisiness?
FWIW, the bottom cover and case are off.
Since the noises are only in one channel the problem is not in the power supply. I would still suggest replacing the remaining PS caps. As I suggested earlier, use individual caps. Replacement cans are very expensive.
Since volume, bass, treble or input choice has no effect, the problem is after those.
Most likely you have noisy resistors and/or bad solder joints. The carbon comp resistors used in vintage gear don't age well. Their values drift higher due to heat exposure and humidity.
I'd start by replacing all the resistors in the output section of the left channel.
Yes, in hindsight I realized that a problem with the PS would affect both channels.
And I also agree that changing out the carbon comp resistors would be a good idea. And I may do that still but for the moment, I may have had a bit of luck.
This morning, I installed a brand new quad of 6BQ5's. What I had been using were some Russian 6P14P's with unknown providence.
The noise issue has all but disappeared provided that a signal source is connected to that input. The sputtering/chattering sound has not reoccurred and as just mentioned, the "rushing" noise is gone as long as something is connected to that pair of inputs.
I see no reason why some shorting plugs that I can make will not eliminate that sound from inputs should there be nothing connected. Or, just not be concerned if there's noise from unused jacks.
One 12AX7 is more microphonic than it's partner but a world away from the microphonics exhibited when the 6P14P's were in place.
I will be obtaining one more tube for the radio portion - a 6BL8 aka ECF80. The one included in the batch of used tubes I bought at the outset, had a leak.
The next time I have $40 burning a hole in my pocket, I may buy two 12AX7's locally. And, as time allows, I will start recording the values of the carbon comp resistors. An least now, without all the old capacitors in the way, there is more room to view the banding.
I've been doing my "evaluating" with a cassette deck and mostly through headphones. Not a connoisseur, but it sounded good to me. Speakers too but just a pair of Minimus 7's and sound was as good as they allowed. Later today, I shall haul over a turntable and see how that works out.
And I also agree that changing out the carbon comp resistors would be a good idea. And I may do that still but for the moment, I may have had a bit of luck.
This morning, I installed a brand new quad of 6BQ5's. What I had been using were some Russian 6P14P's with unknown providence.
The noise issue has all but disappeared provided that a signal source is connected to that input. The sputtering/chattering sound has not reoccurred and as just mentioned, the "rushing" noise is gone as long as something is connected to that pair of inputs.
I see no reason why some shorting plugs that I can make will not eliminate that sound from inputs should there be nothing connected. Or, just not be concerned if there's noise from unused jacks.
One 12AX7 is more microphonic than it's partner but a world away from the microphonics exhibited when the 6P14P's were in place.
I will be obtaining one more tube for the radio portion - a 6BL8 aka ECF80. The one included in the batch of used tubes I bought at the outset, had a leak.
The next time I have $40 burning a hole in my pocket, I may buy two 12AX7's locally. And, as time allows, I will start recording the values of the carbon comp resistors. An least now, without all the old capacitors in the way, there is more room to view the banding.
I've been doing my "evaluating" with a cassette deck and mostly through headphones. Not a connoisseur, but it sounded good to me. Speakers too but just a pair of Minimus 7's and sound was as good as they allowed. Later today, I shall haul over a turntable and see how that works out.
Seems the right channel in the phono section is all but dead. Turntable is not the cause so back to the schematic I go and do some poking and prodding. Hopefully something will reveal itself. Already tried swapping pre-amp tubes without change.
If I cannot determine a fault, I may start another thread specific to that. This one, concerning to the power amplifier was successful and I thank all who contributed.
If I cannot determine a fault, I may start another thread specific to that. This one, concerning to the power amplifier was successful and I thank all who contributed.
Fifteen months later, and following a city to rural move, I took to having another go at making this receiver work.
One blunder back then created by yours truly, of imperfectly soldering one of the new capacitors, seems to have been the main reason why one channel was out on MAG PHONO. It took the fresh pair of a new housemate's eyes to spot it.
And thanks to who knows, a 100 ohm resistor that should have been a 1.5K ohm.
Plus two original plate resistors that read OL and another of unknown purpose that I broke in two.
Just recently sorted the resistor issues out and other than some background hum with phono volume up high and crummy radio reception, it is working pretty well. There's no AM around here to speak of and an antenna might help with FM.
This is the first piece of tube anything I've used for listening to records since the 1960's. For what it is, and the level I am listening at, I quite like it. It's satisfyingly different.
There is some righteous heat at the back right corner. Probably the ouput tubes in conjuction with some serious looking wire wound resistors on the chassis' underside. There are chassis holes right above them to allow heat to rise and escape. Would keep my coffee nicely warm when I'm parked at this computer.
One blunder back then created by yours truly, of imperfectly soldering one of the new capacitors, seems to have been the main reason why one channel was out on MAG PHONO. It took the fresh pair of a new housemate's eyes to spot it.
And thanks to who knows, a 100 ohm resistor that should have been a 1.5K ohm.
Plus two original plate resistors that read OL and another of unknown purpose that I broke in two.
Just recently sorted the resistor issues out and other than some background hum with phono volume up high and crummy radio reception, it is working pretty well. There's no AM around here to speak of and an antenna might help with FM.
This is the first piece of tube anything I've used for listening to records since the 1960's. For what it is, and the level I am listening at, I quite like it. It's satisfyingly different.
There is some righteous heat at the back right corner. Probably the ouput tubes in conjuction with some serious looking wire wound resistors on the chassis' underside. There are chassis holes right above them to allow heat to rise and escape. Would keep my coffee nicely warm when I'm parked at this computer.
Attachments
Eli was right . . .
increasing those coupling capacitor values might cause your amplifier to be an oscillator / motor-boater.
Improvements of amplifiers that employ negative feedback is tricky.
If I were changing something, I would change the single self bias resistor that is connected to all 4 output tubes.
I would use 4 individual self bias resistors, and 4 individual bypass electrolytic capacitors.
Electrolytic caps are smaller size these days for the same capacitance and same voltage rating. Use 4 resistors that are each 4 times the original single resistance.
You probably do not have the room to do that (but try really hard to find the space).
Or . . .
Be sure to get output tubes that are Extremely Well Matched at the exact quiescent voltage and quiescent current of your amplifier.
Individual Self Bias,
Or
Extremely Well Matched tubes,
Will keep the currents in the output transformers balanced. They will not suffer from early saturation and early distortion.
Forget what I said above.
Boy, did I mess up.
The amplifier uses the same darned scheme as my old Harmon Kardon A300.
They used the output tubes cathode current to run the preamp tube filaments.
If you take out the phono section, and then calculate the total resistance (with the preamp tube filaments hot, not cold),
you can use individual self bias; the resistors are 4X the original resistance of the resistors and filaments in the cathode circuit.
With the preamp removed, there is room for the 4 resistors and 4 bypass caps.
increasing those coupling capacitor values might cause your amplifier to be an oscillator / motor-boater.
Improvements of amplifiers that employ negative feedback is tricky.
If I were changing something, I would change the single self bias resistor that is connected to all 4 output tubes.
I would use 4 individual self bias resistors, and 4 individual bypass electrolytic capacitors.
Electrolytic caps are smaller size these days for the same capacitance and same voltage rating. Use 4 resistors that are each 4 times the original single resistance.
You probably do not have the room to do that (but try really hard to find the space).
Or . . .
Be sure to get output tubes that are Extremely Well Matched at the exact quiescent voltage and quiescent current of your amplifier.
Individual Self Bias,
Or
Extremely Well Matched tubes,
Will keep the currents in the output transformers balanced. They will not suffer from early saturation and early distortion.
Forget what I said above.
Boy, did I mess up.
The amplifier uses the same darned scheme as my old Harmon Kardon A300.
They used the output tubes cathode current to run the preamp tube filaments.
If you take out the phono section, and then calculate the total resistance (with the preamp tube filaments hot, not cold),
you can use individual self bias; the resistors are 4X the original resistance of the resistors and filaments in the cathode circuit.
With the preamp removed, there is room for the 4 resistors and 4 bypass caps.
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Thank you for the suggestion but removing the pre-amp section is not something I would consider doing. In it's present state, this receiver works well enough for my needs which does involve a turntable. I realize I could do so with an outboard phono pre-amp but my preference would be having the receiver function in it's entirety.
Regarding output tubes, in April, 2019 I posted of having obtained a quad of brand new Sovtek 6BQ5's from Jim McShane. I corresponded with him beforehand and he offered to send a set which he referred to as "cool matched".
I am thinking that would address your "extrememly well matched tubes" recommendation?
I have not listened to music through tube amplification since circa 1970 (other than AM broadcast through a Heathkit amp/tuner combo) therfore I have nothing to reference how this receiver should sound. But what I have heard so far in the few hours I've listened to it with phono and and CD as a source, is not objectionable at all. I actually enjoy what I am hearing more so than through the small Akai integrated (AM-2350) that was in place.
Whether or not it hangs together for the long run, I cannot say. I will cross that bridge later if the time comes.
But thanks again, for the thoughts and taking the time to post.
With your meter set in the 200 mA range, probe across all four output transformer primary windings' halves. Your tubes are sufficiently matched if you get four almost identical readings.
If they aren't, pair each two tubes with close readings.
Btw, there's an error in the schematics: Never try to replace V12 by an ECL80!
Best regards!
If they aren't, pair each two tubes with close readings.
Btw, there's an error in the schematics: Never try to replace V12 by an ECL80!
Best regards!
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