i just won a couple heathkit w-3m amplifiers on ebay from two different sellers (they havent gotten here yet), right now i am on deployment with the uss ronald reagan aircraft carrier and being at sea for a over a month at a time with not much work to do, i needed a little project to keep me sane. since they came from two different sellers i'm pretty sure i'm looking at basicly rebuilding both of them, replacing some resistors, all capacitors, suck out and replace all of the old solder and replace the tubes on one to match them up. this will be my first time doing this much work to a tube amp, the most i've done is just a little tinkering here and there with my sherwood S5500III.
that being said, i havnt really found much info on these amps on the web and i havnt found any info about rebuilding them. so i'm here for advice. does anyone have any suggestions as far as upgrades, modifications, changes in the circuit, and which old components should be replaced with newer and better parts? have any of you already rebuild one? how did it come out? any help would be great.
the manual can be found here with the best schematic i've found for it.
thanks, kyle.
that being said, i havnt really found much info on these amps on the web and i havnt found any info about rebuilding them. so i'm here for advice. does anyone have any suggestions as far as upgrades, modifications, changes in the circuit, and which old components should be replaced with newer and better parts? have any of you already rebuild one? how did it come out? any help would be great.
the manual can be found here with the best schematic i've found for it.
thanks, kyle.
hey-Hey!!!,
I'd suggest upping the voltage on the amp-chassis B+ capacitors to 500V. Digikey's snap-in Panasonic will be good there, and you can up the capacitance w/o endangering the tube rectifier.
As to the circuit, I'd suggest cleaning the amps, restoring them and *THEN* worry about modification. On that front, there are many ways to skin the cat, yes?
cheers,
Douglas
I'd suggest upping the voltage on the amp-chassis B+ capacitors to 500V. Digikey's snap-in Panasonic will be good there, and you can up the capacitance w/o endangering the tube rectifier.
As to the circuit, I'd suggest cleaning the amps, restoring them and *THEN* worry about modification. On that front, there are many ways to skin the cat, yes?
cheers,
Douglas
good idea, safety upgrade!
but as far as mods, i dought that both amps will be the same inside, one of them looks like it had a re-cap done (they used 450V caps) and i want to match them up for a dual mono setup, might as well upgrade the parts that i'm changing while i'm at it.
another thing of concern, the manual states on first startup that there will be background noise and this indicates normal operation. i wonder how much noise there is and if i can silence that noise? i guess i'll have to wait till they get here.
but as far as mods, i dought that both amps will be the same inside, one of them looks like it had a re-cap done (they used 450V caps) and i want to match them up for a dual mono setup, might as well upgrade the parts that i'm changing while i'm at it.
another thing of concern, the manual states on first startup that there will be background noise and this indicates normal operation. i wonder how much noise there is and if i can silence that noise? i guess i'll have to wait till they get here.
well i finally got my amps a while ago and i've been slowly rebuilding them as my mail comes in (military mail takes forever!) and after seeing how many people looked at this thread without posting, it seems like there is some interest in these amps. so far i've completely gutted one amp and power supply, cleaned them up and installed all new wire, resistors, and caps (except for the signal caps, the new ones havnt come in the mail yet). even tho i am using an old sony radio speaker in a cardboard and duct tape encloser, it sounds really good, very clean sound with no background noise that i can hear. but i do have a couple problems.
first problem, when i replaced the capacitors in the power supply, the voltages went up, where the voltage should be 440vdc +/- 20% with a line voltage of 105-125 (my ships voltage is at 120vac), after changing the caps i get 466vdc. a bit high. with the old caps the voltage was arround 450vdc. so why did the voltage go up? i replaced the 20uf caps with 22uf and the 50uf with 68uf panasonic ecg caps. this raise in voltage is causing the two 47K 2W matched resistors to get VERY hot, the blue ceramic coating on them has browned a bit. also the bias current went up, the heathkit manual says that bias should be between 40 and 60 mA, before i changed the power supply caps it was arround 61mA, a bit high, but not too bad. now it reads 74mA so why the increase? did i miss something?
the other problem that i have is when i turn the amp on, after a few seconds i get the "motorboat" sound for about a second and for about 5 minuites when it is playing music, the quieter bass gets a bit of static. it could be the signal caps, but i wont really be able to find out untill i get the new ones.
anyways here are some pictures from when i got them and after some cleaning, i'll post some more later.
first problem, when i replaced the capacitors in the power supply, the voltages went up, where the voltage should be 440vdc +/- 20% with a line voltage of 105-125 (my ships voltage is at 120vac), after changing the caps i get 466vdc. a bit high. with the old caps the voltage was arround 450vdc. so why did the voltage go up? i replaced the 20uf caps with 22uf and the 50uf with 68uf panasonic ecg caps. this raise in voltage is causing the two 47K 2W matched resistors to get VERY hot, the blue ceramic coating on them has browned a bit. also the bias current went up, the heathkit manual says that bias should be between 40 and 60 mA, before i changed the power supply caps it was arround 61mA, a bit high, but not too bad. now it reads 74mA so why the increase? did i miss something?
the other problem that i have is when i turn the amp on, after a few seconds i get the "motorboat" sound for about a second and for about 5 minuites when it is playing music, the quieter bass gets a bit of static. it could be the signal caps, but i wont really be able to find out untill i get the new ones.
anyways here are some pictures from when i got them and after some cleaning, i'll post some more later.
Attachments
Those 47K resistors in Williamson designs are known to get quite hot. It's probably best to change each 47K, 2W resistor to two 100K, 2W resistors in parallel for more power dissipation abilities. 466VDC for the B+ is close enough to 440 for no problems, they probably measured theirs (on page 18) with 110-115VAC on the input. Nice set of amps there!, I didn't know you could work on this kind of hobby stuff at sea.
yea, i was thinking of replacing those resistors with either higher watt resistors or two 100k as you suggested, i just wasnt sure if there was something wrong or if it is just supposed to be that way. but they dont really care about working on hobbies here as long as i have enough room to put it away. i'm an IC (interior communications electrician) so we always have some sort of electronic gear being ripped appart in here anyways.
Do you have equalizing resistors in parallel with the series connected caps?
In this picture it appears that the caps are connected in series,but I don't see any resistors:
http://www.diyaudio.com/forums/attachment.php?attachmentid=140740&d=1252786047
In this picture it appears that the caps are connected in series,but I don't see any resistors:
http://www.diyaudio.com/forums/attachment.php?attachmentid=140740&d=1252786047
sounds like a good idea, i'll have to wait till i get back from deployment tho, the only supplies i had were what i needed to rebuild these amps and mail takes forever. is this what you mean? but you are right, the voltage on the caps is not even, but it stays at least 50v below maximum rated for each cap.
edit: yes i know, i drew the curved line on the electrolytic caps backwords.
edit: yes i know, i drew the curved line on the electrolytic caps backwords.
W3a
Hi:
Those jacks in the cathodes of the output tubes are for measuring the currents in the output tubes. Use a DC miliammeter at least 200 ma full scale. You can increase the value of the single resistor, 700 ohm 7 watts , that connects to the two 100 ohm resistors. Try 750 or 800 ohms 10 WATTS to lower the current through the outputs.
Adjust the 100 ohm pot in the cathode circuit for equal readings on the meter that plugs into the jacks for each tube.
To make the current readings a lot easier put a 10 ohm 5 watt resistor in each output cathode lead , jack to ground. This will allow you to measure current , Ohms Law , and will allow easy balancing of the tube currents , hook the meter from cathode to cathode and adjust the 100 ohm balance pot for ZERO voltage.
Hope this helps
Ed
Hi:
Those jacks in the cathodes of the output tubes are for measuring the currents in the output tubes. Use a DC miliammeter at least 200 ma full scale. You can increase the value of the single resistor, 700 ohm 7 watts , that connects to the two 100 ohm resistors. Try 750 or 800 ohms 10 WATTS to lower the current through the outputs.
Adjust the 100 ohm pot in the cathode circuit for equal readings on the meter that plugs into the jacks for each tube.
To make the current readings a lot easier put a 10 ohm 5 watt resistor in each output cathode lead , jack to ground. This will allow you to measure current , Ohms Law , and will allow easy balancing of the tube currents , hook the meter from cathode to cathode and adjust the 100 ohm balance pot for ZERO voltage.
Hope this helps
Ed
yea, thats already in the plans, but i need to wait till i get back from deployment and see what the line voltage is at my house, it may be lower then here on the ship and bring the current back down to where it should be. but if not, then i'll be doing some resistor swapping. your probubally talking about the 250 ohm 7w resistor tho? right now they are 250 ohm 10w and they still get pretty hot, so i'll be looking at upping the wattage on them anyways just to make sure nothing goes pop.
i may try out your method of bias sometime in the future tho, not sure tho, it is actually very easy to set as is, it takes longer to get out the 1/4" plug, aligator clip meter leads and set it up then it does to match up the bias.
thanks, kyle.
i may try out your method of bias sometime in the future tho, not sure tho, it is actually very easy to set as is, it takes longer to get out the 1/4" plug, aligator clip meter leads and set it up then it does to match up the bias.
thanks, kyle.
i've got a problem... i think i may have blown my OPT on one of the amps... i had music playing for about an hour, all was fine and sounded great, then i switched speakers and the sound became very static and rough, i happened to look over at the rectifier tube and the plates were glowing orange and a few small sparks flew and then the 3 amp fuse popped. i disconnected everything and tested the power supply by itself, it works fine. then i hooked up the amp w/o tubes and it popped another fuse. hooked up the other amp chasis and it works fine. i took some resistance readings and compared between the two amps and on the OPT at grid 2 and plate on the power tubes where i read about 1 Megaohm to ground on the good amp i am now reading arround 250 ohm to ground.
the only differances from how i had them running before and now, i got my .25uf caps and new output tubes. the caps are russian mbm pio caps rated at 250V. when the amps are running they see about 156vdc each, they did not get hot and they still test the same as they did new in capacitance and resistance. the tubes i was using are russian 6P3S-E, these are supposed to be a direct replacement for 5881/6L6GC. the new tubes also had a very faint blue glow to them. not sure if this is normal or not. but bias current on these was slightly lower then the 5881. so what would have caused my OPT to short like this? and how can i make sure that it doesnt happen again?
the only differances from how i had them running before and now, i got my .25uf caps and new output tubes. the caps are russian mbm pio caps rated at 250V. when the amps are running they see about 156vdc each, they did not get hot and they still test the same as they did new in capacitance and resistance. the tubes i was using are russian 6P3S-E, these are supposed to be a direct replacement for 5881/6L6GC. the new tubes also had a very faint blue glow to them. not sure if this is normal or not. but bias current on these was slightly lower then the 5881. so what would have caused my OPT to short like this? and how can i make sure that it doesnt happen again?
i have now definately narrowed the problem down to a bad OPT... on the good one i read 152 ohm from red to blue/white and 80ohm between blue/white and green/white. on the bad one i read 411ohm from red to blue/white and 342ohm between blue/white and green/white.
not sure if it was a good idea or not, but i powered up the chasis with out the transformer in the loop and it powered up fine and did not blow any fuses. did the same with the other amp with the transformer out of hte loop and got the same voltage readings. any suggestions for a good transformer to replace my acrosound? maybe something a little tougher so it doesnt break again? maybe an edcor CXPP45-MS-6.6K?
not sure if it was a good idea or not, but i powered up the chasis with out the transformer in the loop and it powered up fine and did not blow any fuses. did the same with the other amp with the transformer out of hte loop and got the same voltage readings. any suggestions for a good transformer to replace my acrosound? maybe something a little tougher so it doesnt break again? maybe an edcor CXPP45-MS-6.6K?
Did you turn the amp off while switching speakers?
Those 6P3S-E's are supposed to be tough as nails. The blue glow is perfectly normal.
Jeff
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