Hello everyone, I am just hoping to get a little help and advice on rebuilding my recently acquired Pioneer SA-810 tube amp..
I picked it up off eBay, it was a bit of a blind buy with no inside pictures and little info but I'm really happy with it so far.
I believe it has had some work done at some stage as there were some odd caps in there, resistors replaced etc. but this was done a long time ago..I am hoping that it maybe had tubes refreshed at some stage.
So I am now learning tube gear. I have done a lot of solid state repairs and rebuilds but I'm new to valve amplifier circuits so please go easy on me..
Right, So far I have replaced all electrolytic caps, including almost all of the can caps.. the one left is probably the worse one showing signs of heat at the bottom..its 40uF x2 450V.. I ordered some replacement parts with intention of locating new caps under chassis but there is very little room and I think I am going to re order and maybe stuff the old cap. despite its questionable condition i have no hum.
there are two 100uF 350v high ripple current rated i have replaced, I replaced with some caps i had already, but i need to re order some with lower ESR higher ripple current rating i think.
I have replaced almost all other caps with Panasonic film..I am now studying signal path etc and may change some of these out later.
The reason I am asking for some help is, I now have a white noise issue..
if i turn the treble pots up full its loud on both channels evenly..
I am now looking at replacing all the CC resistors as many of them have drifted high.. and maybe even the treble pots as one is a bit sandy like..
So I'm thinking of replacing all CC's with metal films apart from grid stoppers..
thoughts?
and when we talk about noise in resistors, just how much to the ear can they give? its a fair hiss i have on both channels with treble pots at full..which makes me wonder if i have bad tubes...I hope these are not needle in a hay stack questions.. what ever is causing the noise it is definitely not normal, it is loud enough to come over the top of music.. it does not increase with volume.
I picked it up off eBay, it was a bit of a blind buy with no inside pictures and little info but I'm really happy with it so far.
I believe it has had some work done at some stage as there were some odd caps in there, resistors replaced etc. but this was done a long time ago..I am hoping that it maybe had tubes refreshed at some stage.
So I am now learning tube gear. I have done a lot of solid state repairs and rebuilds but I'm new to valve amplifier circuits so please go easy on me..
Right, So far I have replaced all electrolytic caps, including almost all of the can caps.. the one left is probably the worse one showing signs of heat at the bottom..its 40uF x2 450V.. I ordered some replacement parts with intention of locating new caps under chassis but there is very little room and I think I am going to re order and maybe stuff the old cap. despite its questionable condition i have no hum.
there are two 100uF 350v high ripple current rated i have replaced, I replaced with some caps i had already, but i need to re order some with lower ESR higher ripple current rating i think.
I have replaced almost all other caps with Panasonic film..I am now studying signal path etc and may change some of these out later.
The reason I am asking for some help is, I now have a white noise issue..
if i turn the treble pots up full its loud on both channels evenly..
I am now looking at replacing all the CC resistors as many of them have drifted high.. and maybe even the treble pots as one is a bit sandy like..
So I'm thinking of replacing all CC's with metal films apart from grid stoppers..
thoughts?
and when we talk about noise in resistors, just how much to the ear can they give? its a fair hiss i have on both channels with treble pots at full..which makes me wonder if i have bad tubes...I hope these are not needle in a hay stack questions.. what ever is causing the noise it is definitely not normal, it is loud enough to come over the top of music.. it does not increase with volume.
Another question I have about this amplifier is 4 ohm speaker compatibility? I actually purchased it to drive specific speakers after reading somewhere its 60W into 8ohm and 30W into 4.. it only has 8 and 16 Ohm taps.. I have recently learnt impedance matching makes a huge difference to the sound of a valve amp..
There is no need for "Low ESR" capacitors, it is a valve amplifier with only a low current draw. Low ESR is for high demand SS amplifiers and systems.
The hiss is possibly noisy ECC83/12AX7WA valves but may be the anode load resistors.
If you remove the phono pre amp valves and the hiss stops, it could be because there is no input.
The hiss is possibly noisy ECC83/12AX7WA valves but may be the anode load resistors.
If you remove the phono pre amp valves and the hiss stops, it could be because there is no input.
White noise and hum when the input is left unconnected is normal. Be sure to short any unused high gain input.
On a similar amplifier, I once replaced all the carbon resistor with 1W metal films and the background white noise improved. Some preamp tubes are noisy, you may also try to replace them.
I checked your amplifier schematic, and some audible white noise is probably there by the way is designed: high preamp gain plus high impedence potentiometers means background white noise, usually. You may also hear a very faint hum while touching knobs on the faceplate, this is also a common issue on some consumer grade amplifiers of that era. By the way, you will not keep the treble control all the way up on regular listening sessions, so I would not be worried by the issue.
Replacement of multisection main filter capacitors is always a struggle, because exact modern replicas are expensive and hard to source. You may order them on the website Frag´ Jan Zuerst - Ask Jan First GmbH & Co. KG : go to the catalog section and prepare yourself for a sticker shock. According to my experience, most high quality Japan and EU equipments built in the late '60 don't need the main filter caps replaced straight away, or at least only the first one will check as severely degraded. The other sections will often check as mildly degraded and slightly leaky, but still effective. Absence of power supply hum is a further indication that there is no immediate danger of catastrophic failure. When the replacement with modern capacitors is difficult, or it may deface the amplifier, I leave the original filter capacitors in place and put a low amperage fuse on the HT secundary winding (100-400 mA, according to the needs). It will protect the transformer from sudden capacitor failures while I evaluate if the replacement or restuffing is worth the expense and hassle.
On a similar amplifier, I once replaced all the carbon resistor with 1W metal films and the background white noise improved. Some preamp tubes are noisy, you may also try to replace them.
I checked your amplifier schematic, and some audible white noise is probably there by the way is designed: high preamp gain plus high impedence potentiometers means background white noise, usually. You may also hear a very faint hum while touching knobs on the faceplate, this is also a common issue on some consumer grade amplifiers of that era. By the way, you will not keep the treble control all the way up on regular listening sessions, so I would not be worried by the issue.
Replacement of multisection main filter capacitors is always a struggle, because exact modern replicas are expensive and hard to source. You may order them on the website Frag´ Jan Zuerst - Ask Jan First GmbH & Co. KG : go to the catalog section and prepare yourself for a sticker shock. According to my experience, most high quality Japan and EU equipments built in the late '60 don't need the main filter caps replaced straight away, or at least only the first one will check as severely degraded. The other sections will often check as mildly degraded and slightly leaky, but still effective. Absence of power supply hum is a further indication that there is no immediate danger of catastrophic failure. When the replacement with modern capacitors is difficult, or it may deface the amplifier, I leave the original filter capacitors in place and put a low amperage fuse on the HT secundary winding (100-400 mA, according to the needs). It will protect the transformer from sudden capacitor failures while I evaluate if the replacement or restuffing is worth the expense and hassle.
I mentioned low ESR is because i believe caps rated with high ripple current ratings are low ESR.. Anyway, the ones i pulled out are probably still in good condition, they measured on my Peak meter at 135uF and 0.14 Ohm.
the replacements have a ripple current rating of 986.7mA @ 50kHz
is this enough?
i might do some valve shuffling with some spare 12ax7 i have today and see what happens.
i didn't even think of shorting the phono inputs.. will try that also thank you.
so would you say replacing all CC's with metal films is the way to go? also would replacing the pots clean things up? Yes I have another pioneer receiver tube amp i have re capped and left the old can caps in place..I like that fuse idea i might try it with that one.. one of the can caps i have pulled from this one is measuring low on capacitance though..its a 40 20 20 uf and ive got 30 15 15 uf, I have manage to locate a 47 and 2x 22uF caps under chassis to replace. to do that i had to shift the 2 16 Ohm 7W resistors that run off the secondary of the output transformers..
the original diodes are in place put i do have some new ones on my list of parts to order..
the capacitors replaced are all very close to original spec i believe..
I do not have a tube tester, I am trying to find someone local capable of testing all my tubes now..
It worked for 40 years with whatever ESR caps had in those days. It does NOT need "new-think".
If it hisses evenly both sides with controls full up, turn it down! And connect a good signal source. Bad carbon-comp resistors hiss like killer bees but never the same both sides. Good comp resistors hiss a little more than film caps, but not to ruin the music.
_IF_, after some months of use, you decide this is THE amp for you forever, _then_ think about "upgrades". If it really needs it.
If it hisses evenly both sides with controls full up, turn it down! And connect a good signal source. Bad carbon-comp resistors hiss like killer bees but never the same both sides. Good comp resistors hiss a little more than film caps, but not to ruin the music.
_IF_, after some months of use, you decide this is THE amp for you forever, _then_ think about "upgrades". If it really needs it.
Lets just forget i mentioned ESR 
when i say both sides i mean the symptom is the same both channels.. just that old TV between channels kinda sound but it is individual probably down to the tubes. With both treble pots at anywhere over half..volume pot does not adjust volume of sound.. It has to go.. I have been listening to the amplifier today and it sound really good..but this distortion isn't a tube thing I am sure its a fault in circuit.
I had the schematic blown up and printed onto A3 today to help me read it. Something i didn't mention is when switching the high/low bypass filters the circuit is not happy. I get an audible pop when flicking these switches..although old they are pretty well sealed and i don't think its a case of being dirty.. I am looking at 2 330pF caps in this circuit off the grid pin 7 of the 12ax7 wondering if they are bad as i have not replaced them..I would actually eliminate these switches if i could as i don't see any use for them.
when i say both sides i mean the symptom is the same both channels.. just that old TV between channels kinda sound but it is individual probably down to the tubes. With both treble pots at anywhere over half..volume pot does not adjust volume of sound.. It has to go.. I have been listening to the amplifier today and it sound really good..but this distortion isn't a tube thing I am sure its a fault in circuit. I had the schematic blown up and printed onto A3 today to help me read it. Something i didn't mention is when switching the high/low bypass filters the circuit is not happy. I get an audible pop when flicking these switches..although old they are pretty well sealed and i don't think its a case of being dirty.. I am looking at 2 330pF caps in this circuit off the grid pin 7 of the 12ax7 wondering if they are bad as i have not replaced them..I would actually eliminate these switches if i could as i don't see any use for them.
Ok, I went and purchased some decent high voltage clip on probes yesterday and done what i should have done first thing and that's check voltages. I have low B+ measurements which sent me into panic mode thinking I may have a bad transformer. Even with variac and dimb bulb tester
So I went back across all my work marking everything off on the schematic looking for current leakage. I also replaced some out of spec resistors and the diodes.
I cannot find any faults. I have also now replaced the one remaining Can capacitor with 2 fresh caps.
I am worried about powering it up now even to check voltages as i don't want to blow a transformer.
Measurements I have taken are
PIN 1 and 6 of 12ax7 are nearly dead on 140V which is correct
PIN 6 of 6AN8 89V , should be 85V
PIN 1 of 6AN8 160V , should be 275V
PIN 9 of 7868 285V , should be 420V
I have been across the power supply and filter caps 3 times checking everything which is all correct i believe. I have low measurements here at each filter cap junction.
So I believe there is excess current going somewhere...
Should I stop now and get the 6AN8's tested? or should i be putting an Amp meter in series with these B+ taps to find exactly where the current is going?
I am still going across circuit now looking for anything I may have missed.
Am I one the right path here?
So I went back across all my work marking everything off on the schematic looking for current leakage. I also replaced some out of spec resistors and the diodes.
I cannot find any faults. I have also now replaced the one remaining Can capacitor with 2 fresh caps.
I am worried about powering it up now even to check voltages as i don't want to blow a transformer.
Measurements I have taken are
PIN 1 and 6 of 12ax7 are nearly dead on 140V which is correct
PIN 6 of 6AN8 89V , should be 85V
PIN 1 of 6AN8 160V , should be 275V
PIN 9 of 7868 285V , should be 420V
I have been across the power supply and filter caps 3 times checking everything which is all correct i believe. I have low measurements here at each filter cap junction.
So I believe there is excess current going somewhere...
Should I stop now and get the 6AN8's tested? or should i be putting an Amp meter in series with these B+ taps to find exactly where the current is going?
I am still going across circuit now looking for anything I may have missed.
Am I one the right path here?
The little tubes CAN'T suck big current' cuz they are little, and cuz they have large resistances in series.
Don't even be looking there. Pull the BIG bottles, and look around the power supply.
+ of C49 should be over 420V. Report actual value.
However, both C49 C50 must be "good" to get proper voltages. If they are old, they may be replaced on general distrust.
Also verify voltage at C51 is in the ballpark (and negative!).
Don't even be looking there. Pull the BIG bottles, and look around the power supply.
+ of C49 should be over 420V. Report actual value.
However, both C49 C50 must be "good" to get proper voltages. If they are old, they may be replaced on general distrust.
Also verify voltage at C51 is in the ballpark (and negative!).
