hi, i'm just out of noob school and have a problem with an old heathkit s99 amp. I accidently cut off air vents to the amp one evening and started to inhale a strange smell. Being slow off the mark, the amp died. There is plenty of wax drippings on the chassis now under the mains transformer that was not there previously. I have measured the voltage straight out of the transformer before the gz34 and there is no voltage. I didn't think transformers died this way? Now i'm thinking to replace the transformer and assume the output voltage is not that important as long as it is close? And i have no idea of the current demands (mA).?
I have aquired a schematic of the s88 which i'm told is identical apart from the fact that my amp has better quality OPT's. Am i right in saying that i can dispense with the preamp side of this amp and just send my line in into the volume pot? making it a power amp? I'm at a loss here as what to do, any suggestions or answers to the ?'s above would be much appreciated... i'm willing to take on some simple modifications too, upgrade caps etc...
I have aquired a schematic of the s88 which i'm told is identical apart from the fact that my amp has better quality OPT's. Am i right in saying that i can dispense with the preamp side of this amp and just send my line in into the volume pot? making it a power amp? I'm at a loss here as what to do, any suggestions or answers to the ?'s above would be much appreciated... i'm willing to take on some simple modifications too, upgrade caps etc...
The schematic you posted shows a power transformer with a 440VCT high voltage secondary. Full wave rectified through the GZ34 you might get 285VDC or so. It was rather nice of them to include a GZ34 in the design - lesser amps might have tried to get away with an EZ81 or something.
Each pair of ECL82 power tubes should probably be drawing somewhere around 70mA. You'll need a little extra for whatever driver tubes you've got in the front end, including the triode section of each ECL82. The EF86 will take ~6mA. The the ECF80 could take as much as 28mA, but I can't imagine it would be running that hard given its position in the circuit. If you can find a PT rated for ~200mA, I'd expect it would be more than adequate.
You'll need 2A at 5.0 volts to power the heater in the GZ34. You'll also need a 6.3V winding on the PT. Again, if you stay with the tubes shown in the schematic you would need at least 4.5 amps (ECL82 needs 0.78A, EF86 needs 0.2A, ECF80 needs 0.45A).
Each pair of ECL82 power tubes should probably be drawing somewhere around 70mA. You'll need a little extra for whatever driver tubes you've got in the front end, including the triode section of each ECL82. The EF86 will take ~6mA. The the ECF80 could take as much as 28mA, but I can't imagine it would be running that hard given its position in the circuit. If you can find a PT rated for ~200mA, I'd expect it would be more than adequate.
You'll need 2A at 5.0 volts to power the heater in the GZ34. You'll also need a 6.3V winding on the PT. Again, if you stay with the tubes shown in the schematic you would need at least 4.5 amps (ECL82 needs 0.78A, EF86 needs 0.2A, ECF80 needs 0.45A).
Last edited:
As you are in the UK, SOWTER AUDIO TRANSFORMERS is an immediate source but bit expensive. Currently I run an ECL82 p-p amp and it's a darned good sounder. Don't bin it.
The fact you didn't mention the condition of anode ww series resistors of the rectifier, leads me to believe the problem could be a short in the heater winding. What do they look like ?
richy
The fact you didn't mention the condition of anode ww series resistors of the rectifier, leads me to believe the problem could be a short in the heater winding. What do they look like ?
richy
thanks rich
I'll the check the series resistors to the rectifier anodes tonight, I've had the voltmeter on the output of the transformer before the rectifier and i get nothing. would a heater short cause this? there is also the physical observation of a lot of wax leakage that leads me to believe the transformer needs replacing. I've heard of sowter before but was hoping to find a cheap old transformer on ebay that would be close enough in specs to replace. Would love to pick your brains on a possible rebuild/ upgrade of the present circuit.... possibly losing the preamp section?
stuart
I'll the check the series resistors to the rectifier anodes tonight, I've had the voltmeter on the output of the transformer before the rectifier and i get nothing. would a heater short cause this? there is also the physical observation of a lot of wax leakage that leads me to believe the transformer needs replacing. I've heard of sowter before but was hoping to find a cheap old transformer on ebay that would be close enough in specs to replace. Would love to pick your brains on a possible rebuild/ upgrade of the present circuit.... possibly losing the preamp section?
stuart
Hi surfstu,
Have got many a good power transformer off Ebay and have been well pleased.Some of them have been new. The British maker Danbury often come up, these can still be got new. There is also another winder down in the Poole area but I can't remember their name offhand. Will post if the little grey cells will let me
Brgds Bill
Have got many a good power transformer off Ebay and have been well pleased.Some of them have been new. The British maker Danbury often come up, these can still be got new. There is also another winder down in the Poole area but I can't remember their name offhand. Will post if the little grey cells will let me
Brgds Bill
Hi surfstu,
First off despite the length of time I've been lurking about on this site I still regard myself as a noobie.
I have a K502 amp which uses the similar 11bm8 valves ( same as ecl82 but 11v heater supplies ) and it runs around 210v dc on the plates. I'm sure the valves can be pushed a lot harder. It would be best left to someone on this site who has actually built an amp that has pushed the voltage to the limit.
Sorry not to be more helpful but bad advice is worse than no advice at all.
Brgds Bill
First off despite the length of time I've been lurking about on this site I still regard myself as a noobie.
I have a K502 amp which uses the similar 11bm8 valves ( same as ecl82 but 11v heater supplies ) and it runs around 210v dc on the plates. I'm sure the valves can be pushed a lot harder. It would be best left to someone on this site who has actually built an amp that has pushed the voltage to the limit.
Sorry not to be more helpful but bad advice is worse than no advice at all.
Brgds Bill
We did have a 2nd one (the 1st one was so good) ... calling it a Scott might give the wrong impression. It is a PP Class A triode variation on El Cheapo using a Scott LK48 as a donor -- a quite impressive amplifier within its power limitations. The transformer made such a mess, we have just been stripping parts off the dead one as needed.
dave
Attachments
Hi surfstu,
You might find this link interesting
Heathkit S99 valve stereo integrated amplifier - UK Vintage Radio Repair and Restoration Discussion Forum
Brgds Bill
You might find this link interesting
Heathkit S99 valve stereo integrated amplifier - UK Vintage Radio Repair and Restoration Discussion Forum
Brgds Bill
thanks bill, i now have a correct cicuit diagram! Such a shame about the PT, my s99 is far cleaner than the one on the UK vintage repair site. So i need a transformer, a 540V CT. Still unsure about the preamp section of this amp, i built a 12b4 pre with help, as my knowledge is still small, but i was always led to believe that these old preamps were not up to much.
cheers for your help
stuart
cheers for your help
stuart
Hi surfstu,
A 540v ct is the way to go if you want to keep it original.
Once you have this amp up and running it'll be easier to mod.
I'll keep an eye out on Ebay for a tranny and post here
Later if you really want a change perhaps you might like to check out Gingertubes thread on his babey huey amp seeing as your output trannies have got ulralinear taps.If nothing else it's a great read.
Brgds Bill
A 540v ct is the way to go if you want to keep it original.
Once you have this amp up and running it'll be easier to mod.
I'll keep an eye out on Ebay for a tranny and post here
Later if you really want a change perhaps you might like to check out Gingertubes thread on his babey huey amp seeing as your output trannies have got ulralinear taps.If nothing else it's a great read.
Brgds Bill
I'm running them at 280V+ fixed bias at 33mA Iquies per tube with an 8KA-A 40%UL taps expect 8W o/p.
richy
Or not. Rather than pin your hopes on exactly the right PTX coming along here's three suggestions:
1 - get a quote on having your old PTX rewound to original spec. It won't be cheaper, but it will be new and you will know what you have
2 - think about going SS for your rectification and look for a PTX that doesn't need a 5v winding, and doesn't need to be CT. Certainly widens the gene pool.
3 - consider using SEPARATE PTXs - one for B+, another for heaters. Again, widens the pool of candidates.
Whatever you do, if you intend to keep this unit, go bigger rather than on spec or under spec. If the expected load is 200ma, go 250ma for your PTX. Less chance of it dropping wax again....
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.