I got a Philmore sa-2000 and I was wondering if anybody has any information on it or if you have the schematics. There is almost no information on it on the web.
I opened it up and it has 2 x 12ax7 and 4 x 6BM8 in a push-pull setup. All tubes turn on but there is a loud buzz that comes out from the speakers, even at minimum volume. The buz increases slightly at max volume but very little. The heaters are AC. When feeding music through it it is heavily distorded in the low end.
I’m wondering if it’s worth trying to fix or restore it. Does anybody know anything about the quality of this amp? Any schematic out there? I can’t imagine having some unique or proprietary circuit.
Thanks
I opened it up and it has 2 x 12ax7 and 4 x 6BM8 in a push-pull setup. All tubes turn on but there is a loud buzz that comes out from the speakers, even at minimum volume. The buz increases slightly at max volume but very little. The heaters are AC. When feeding music through it it is heavily distorded in the low end.
I’m wondering if it’s worth trying to fix or restore it. Does anybody know anything about the quality of this amp? Any schematic out there? I can’t imagine having some unique or proprietary circuit.
Thanks
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Looks like it is in very nice shape. Probably the two large electrolytic can capacitors need replacement.
This guitar amp circuit may be similar enough in topology to be useful, but the R and C values will likely
differ a lot. The tone circuit will differ also. The output stage and phase inverter may be very close.
This guitar amp circuit may be similar enough in topology to be useful, but the R and C values will likely
differ a lot. The tone circuit will differ also. The output stage and phase inverter may be very close.
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Looks very similar to Lafayette LA-240 or LA-224. Must be the same Japanese producer. Some of these Lafayette some says were produced by Sansui. I had two Lafayette LA-240 and the printouts on the power transformer were identical to the printouts of the power transformers of my Sansui Q-50.
The LA-240 I had sounded really good.
The LA-240 I had sounded really good.
I will reverse engineer, at least the output stage, and compare it with what you provided as well as other 6BM8 circuits on the web.
Should I only replace the electrolytics or all caps? Any idea about the buzz and the heavy distortion? Both channels are identical in buzzing and distortion. I just want to make sure it's not the output transformers. Everything else can be replaced.
Should I only replace the electrolytics or all caps? Any idea about the buzz and the heavy distortion? Both channels are identical in buzzing and distortion. I just want to make sure it's not the output transformers. Everything else can be replaced.
The most likely bad capacitor is the one directly connected to the HV rectifier. This will be a multi-section part,
as seen in the photo. Output transformers are very seldom found to be defective.
After the capacitor is replaced and working, check the values of all the carbon composition resistors, which frequently
drift far off the marked value. Also check the self-bias resistor connected to the output tubes' cathodes, and also
the bypass capacitor across it.
as seen in the photo. Output transformers are very seldom found to be defective.
After the capacitor is replaced and working, check the values of all the carbon composition resistors, which frequently
drift far off the marked value. Also check the self-bias resistor connected to the output tubes' cathodes, and also
the bypass capacitor across it.
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I have a TRIO amp with the same tubes. It has fixed bias. Of course the problem could be the hv electrolytic; I wouldn't be surprised if the problem were the electrolytic after the rectifier ( a small selenium in the TRIO) providing the negative voltage (about minus 20v if I remember well). So replace that one and see what happens.
I have a similar vintage Pioneer amp, with 6AR5 output tubes from memory, and that is chocka full with those Suziki oil caps too. I thought 'oil caps, great!', but they have a bad reputation for reliability and probably need wholesale replacement.
Looks close to the Calrad SA-30B (the earlier SA-30 had one more 12AX7). The similar Monarch SA-40 may be close enough - attached.
Thanks guys for all your input. It looks like the Monarch SA-40 is the closest one. Circuit wise seems to be a match, the only difference being the caps and resistor values which are within 5% of the ones in this Philmore amp.
I've already found a couple of coupling caps, on both channels, that DC was going right through it. Didn't make a difference on distortion or buzz yet but will continue to troubleshoot. Btw, the buzz is 120Hz in case it's any clue to anybody where it might come from.
I'm still not sure whether to invest in recapping it. Does anybody know how the Monarch SA-40 sounds and if it's worth? The caps alone are about $100 Canadian (US $75) and I'm assuming there will be a few resistors as well that drifted quite a bit. I'm not expecting this to be hi-fi btw.
I've already found a couple of coupling caps, on both channels, that DC was going right through it. Didn't make a difference on distortion or buzz yet but will continue to troubleshoot. Btw, the buzz is 120Hz in case it's any clue to anybody where it might come from.
I'm still not sure whether to invest in recapping it. Does anybody know how the Monarch SA-40 sounds and if it's worth? The caps alone are about $100 Canadian (US $75) and I'm assuming there will be a few resistors as well that drifted quite a bit. I'm not expecting this to be hi-fi btw.
What a big difference info and schematic makes. The reason of distortion is because I was using the Tape play input since it was the only one that worked. The other inputs didn't work due to a lose input ground. The tape input and output on this amp is not a tape loop as assumed. It's a tape head input with a sensitivity of 3.5mV. This also explains why the freq response was not flat at all. I'm assuming it's NAB since this is made in Japan. Usually amps that have a tape head input mark it that way not just Tape.
This makes this amp more interesting since I was also working on a different project to build a tape head preamp which didn't go that well.
This makes this amp more interesting since I was also working on a different project to build a tape head preamp which didn't go that well.
Question: The treble pot has a large cap attached to it as seen in the pic. The Monarch schematic has a 0.02u attached to both bass and treble. My amp has a 0.02u attached to bass but it has this monster 0.5u 1000v attached to treble. Should I go with a 0.02u instead of this 0.5u or stick to like for like replacement?
0.5u at 1Kv is hard to source and I'm not sure if this value is the correct one or if someone tinkered with this amp and put a different cap arbitrarily.
0.5u at 1Kv is hard to source and I'm not sure if this value is the correct one or if someone tinkered with this amp and put a different cap arbitrarily.
The nytone sa-2000 is the same exact amp as well. Radiomuseum website has a schematic...but it is hard to make out a lot of the values because the resolution is a bit lacking.
I have one of these nytone versions and it's a nice amp but it did indeed need a lot of caps replaced. I ended up just rebuilding the driver and output stages, got rid of the scheme with the tone controls in the nfb loop, and just ran a direct input to the driver since I didn't need the phono stage. The original schematic reeks of penny pinching imho but the iron seems decent. That said I got it working reliably with no more red plating but never spent much time with it in my main system so can't give a good opinion on the sound.
Edit - elektrotanya.com has a schematic that is much higher resolution and you can make everything out on it.
I have one of these nytone versions and it's a nice amp but it did indeed need a lot of caps replaced. I ended up just rebuilding the driver and output stages, got rid of the scheme with the tone controls in the nfb loop, and just ran a direct input to the driver since I didn't need the phono stage. The original schematic reeks of penny pinching imho but the iron seems decent. That said I got it working reliably with no more red plating but never spent much time with it in my main system so can't give a good opinion on the sound.
Edit - elektrotanya.com has a schematic that is much higher resolution and you can make everything out on it.
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The Nytone SA-2000 is an exact match, even the front plate is very similar except for the brand.
This schematic answers my question regarding the 0.5u cap around the treble pot.
Thanks guys. I'm going for a full recap, maybe some resistors, some 6f3p (6BM8), 6N2P (12ax7 with heater change) and a new 6ca4, probably a Tesla NOS. I know that some if not all the buzz noise comes from the 6BM8 tubes and the caps. Switched tubes around and one of them got hotter than usual and the buzzing subsided by 50%. Basically it needs a complete overhaul.
I'll post here the progress and end results.
This schematic answers my question regarding the 0.5u cap around the treble pot.
Thanks guys. I'm going for a full recap, maybe some resistors, some 6f3p (6BM8), 6N2P (12ax7 with heater change) and a new 6ca4, probably a Tesla NOS. I know that some if not all the buzz noise comes from the 6BM8 tubes and the caps. Switched tubes around and one of them got hotter than usual and the buzzing subsided by 50%. Basically it needs a complete overhaul.
I'll post here the progress and end results.