The Electra-Print OPTs may be a very nice option. I have used Jack's OPTs for several SE amps and they have sounded very nice, especially his Partial Silver Secondary models, but I have never tried a PP.
I think I will start with either the Hammond 1650R (5K) or a vintage Chicago potted OPT (6.6K as I recall) salvaged from old EICO HF-22 amps. I happen to have a spare pair of each of these.
Another possibility is one of the Hashimoto OPTs that are available new. They have a 10K model. A friend has tried a number of OPTs for his PP EL-34 amps and likes the Hashimotos best.
I think I will start with either the Hammond 1650R (5K) or a vintage Chicago potted OPT (6.6K as I recall) salvaged from old EICO HF-22 amps. I happen to have a spare pair of each of these.
Another possibility is one of the Hashimoto OPTs that are available new. They have a 10K model. A friend has tried a number of OPTs for his PP EL-34 amps and likes the Hashimotos best.
Hi - I just looked at the Hashimoto transformers. there is a 10K model rated for 40 watts. If I using the higher voltage configuration of the 124 circuit generating 22 wATTs of power is it OK to have an output transformer that is rated for higher power or it that going to adversely effect performance or be harder to drive? They also have a model HW-25-8 that is 8K primary and rated at 25 watts. I don't know much about this stuff and in the past I have been able to obtain from Hammond transformers that matched exactly the specs of the circuit I was copying.
Hi- I have a few questions about the 124 power supply here: How many watts should the resistor R15.2 (6500 ohms) be rated at? Also R 11 (2500 ohms) watt rating?
Also would it be beneficial to raise the power supply electrolytic filtering a little? If so how much?
One more- What are the specifications of the Western Electric 367A power transformer? And what is the rating in terms of Henrys and current for the W.E. 221 G choke?. I would like to buy comparable new models from Hammond.
Also would it be beneficial to raise the power supply electrolytic filtering a little? If so how much?
One more- What are the specifications of the Western Electric 367A power transformer? And what is the rating in terms of Henrys and current for the W.E. 221 G choke?. I would like to buy comparable new models from Hammond.
Luke,
I like to use Mills wirewound resistors for power supplies so I will probably use Mills 12w for the B+ dropping resistors. You might get by with a 5w but the 12w provides some extra safety margin.
By the way, you don't need to follow the 124 power supply too literally. For the CLC filtering for the output tubes, I generally like equal values for the two capacitors. For example, 50uf---choke---50uf. That is what I plan to try in my amps based on the 124 circuit. I will probably try a small oil cap for the first filter just to be sure, but in past projects I have always preferred equal cap values.
I like to use Mills wirewound resistors for power supplies so I will probably use Mills 12w for the B+ dropping resistors. You might get by with a 5w but the 12w provides some extra safety margin.
By the way, you don't need to follow the 124 power supply too literally. For the CLC filtering for the output tubes, I generally like equal values for the two capacitors. For example, 50uf---choke---50uf. That is what I plan to try in my amps based on the 124 circuit. I will probably try a small oil cap for the first filter just to be sure, but in past projects I have always preferred equal cap values.
Transformer questions
Hi , I have been in touch with Jack at electra print . Here is what he said:
"As for this WE 171C, we can only build a 10K @ 100ma ( if that is the
primary current) to 4 and 8 ohms or one 6 ohm output as our site shows
examples with belends. Electra-Print.com Single-Ended Output Transformers A
single 6 ohm will offer best bandwidth and match 4 and 8 ohms."
I don't know what the current rating for the 171 c is or what current will run through this circuit if if hook the amp up for 20 watts using the higher plate voltage. Do you have any idea of the current here?
Also I was wondering is it is bad to run a 4 ohm speaker from a 6 ohm tap?
I was also wondering if having the transformer wound with silver wire will make a big difference. I have silver speaker cables and I like them but have never heard of silver wire in transformers. I imagine with this option the price will be similar to Hashimoto's transformers at $719 per pair.
I am wondering what you think about these points. Thanks for all your help so far. I am learning a lot about this project now.
Hi , I have been in touch with Jack at electra print . Here is what he said:
"As for this WE 171C, we can only build a 10K @ 100ma ( if that is the
primary current) to 4 and 8 ohms or one 6 ohm output as our site shows
examples with belends. Electra-Print.com Single-Ended Output Transformers A
single 6 ohm will offer best bandwidth and match 4 and 8 ohms."
I don't know what the current rating for the 171 c is or what current will run through this circuit if if hook the amp up for 20 watts using the higher plate voltage. Do you have any idea of the current here?
Also I was wondering is it is bad to run a 4 ohm speaker from a 6 ohm tap?
I was also wondering if having the transformer wound with silver wire will make a big difference. I have silver speaker cables and I like them but have never heard of silver wire in transformers. I imagine with this option the price will be similar to Hashimoto's transformers at $719 per pair.
I am wondering what you think about these points. Thanks for all your help so far. I am learning a lot about this project now.
The 124 schematic shows 19v across the 250R cathode resistor for the output tubes, which is 76ma. Raising the B+ to get more power will increase the current. On my fixed bias amps, I run 6L6GC outputs at 80 to 100ma for the pair. So I think Jack's 100ma spec seems pretty reasonable.
I have some 46 SE amps with Electra-Print OPTs. I used a single-secondary copper OPT for a year or so before getting Jack's Partial Silver Secondary OPTs. Very similar sound quality but slightly faster and cleaner sounding. For just a little more money, the improvement was easily worth it IMO. Jack will also make some OPTs with solid silver wire in the secondaries. I haven't heard any of these but at least one person who has said they have a lighter tonal balance. He preferred the PSS versions.
I have some 46 SE amps with Electra-Print OPTs. I used a single-secondary copper OPT for a year or so before getting Jack's Partial Silver Secondary OPTs. Very similar sound quality but slightly faster and cleaner sounding. For just a little more money, the improvement was easily worth it IMO. Jack will also make some OPTs with solid silver wire in the secondaries. I haven't heard any of these but at least one person who has said they have a lighter tonal balance. He preferred the PSS versions.
It doesn't sound to me like you told him it was a push pull transformer or he didn't look it up. He refers only to his SE line, and if that is all he makes now then I understand the confusion..
A 10K push pull transformer handling several hundred mA of plate current should be a none issue, and you do not need all of the secondaries anyway.
Now I am trying to match the power supply transformer( W.E. 367A) and choke (W.E. 221 G) with a modern equivalent. Do you know the specifications of the western electric 367A power transformer.. - secondary voltage, ma current rating? I can't find this info on line.
Also I found the specifications for the 221 G choke rated at 4.2 H with 80 volts applied @130 ma would this Henry rating change with the voltage that it will see in the power supply of the 124 amp? I am trying to get these specifications so I can order a transformer from Hammond manufacturing THAT WILL Match the power and choke of the W.E. 124 amp that I want to replicate.
Your help would be greatly appreciated. Thanks. Luke Randall
Luke,
The schematic printed in this thread shows the power transformer has 391 VAC on the lower voltage secondary and 426 VAC on the higher voltage tap. Frankly both of those numbers sound high to me given the intended B+ of 384 VDC feeding the output transformer. You can simulate the DC voltage pretty accurately for different PTs and rectifiers with the Duncan power supply program.
The choke inductance is not critical. Something in the 1.5 to 5H range should be fine. You certainly want a max current rating higher than the expected total current draw, but there is no problem having a rating greater than the actual current.
The schematic printed in this thread shows the power transformer has 391 VAC on the lower voltage secondary and 426 VAC on the higher voltage tap. Frankly both of those numbers sound high to me given the intended B+ of 384 VDC feeding the output transformer. You can simulate the DC voltage pretty accurately for different PTs and rectifiers with the Duncan power supply program.
The choke inductance is not critical. Something in the 1.5 to 5H range should be fine. You certainly want a max current rating higher than the expected total current draw, but there is no problem having a rating greater than the actual current.
Last edited:
It seems high to me as well. I am wondering whether the values specified on the schematic despite appearances are actually the open circuit values? This would tend to suggest a fairly high winding DCR.
Note it is a 5U4 and the input capacitor is only 4uF so it is possible that the target voltage is achieved..
The choke seems to have DCR of about 200 ohms based on the stated drop and currents shown in the schematic, this to me implies fairly high inductance. I would probably go for something over 5H as a result were I sticking to the original design intentions.
I think simulating the performance of the supply with PSUD would be advisable to come up with something that works well with modern parts, and performs in a manner analogous to the original which I understand is the intent.
I would strongly recommend looking at the Edcor line of power transformers and chokes as the transformers in particular seem to be MUCH quieter than Hammond, and run a lot cooler. Voltage regulation is rather good too.
Note it is a 5U4 and the input capacitor is only 4uF so it is possible that the target voltage is achieved..
The choke seems to have DCR of about 200 ohms based on the stated drop and currents shown in the schematic, this to me implies fairly high inductance. I would probably go for something over 5H as a result were I sticking to the original design intentions.
I think simulating the performance of the supply with PSUD would be advisable to come up with something that works well with modern parts, and performs in a manner analogous to the original which I understand is the intent.
I would strongly recommend looking at the Edcor line of power transformers and chokes as the transformers in particular seem to be MUCH quieter than Hammond, and run a lot cooler. Voltage regulation is rather good too.
For my own project, which is only loosely based on the 124, I plan to use a slightly different power supply. For the filter caps, I will use 50uf for the first two caps and I will probably use a choke around 1.5 to 2.5H with a lower DCR perhaps in the 20-30 ohm range. I may try an Angela Universal power transformer since I have an extra pair. It has both 320 and 380 secondary windings so I should be able to get close to the WE voltages.
I agree with Kevin about Edcor power transformers. They are very quiet (and so is the Angela) and the voltages are right on the money. Sometimes the Hammonds run a bit higher voltages than the specs indicate.
I agree with Kevin about Edcor power transformers. They are very quiet (and so is the Angela) and the voltages are right on the money. Sometimes the Hammonds run a bit higher voltages than the specs indicate.
This is the correct schematic. Moderator, please delete the earlier drawings with error in post #6 and #44. Thanks.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The L1, 221G choke drops 19v via 99mA so its DCR is 192Ω and
the one that's close in the Hammond catalog is model 159P and its spec is 5H, 125mA, 155Ω DCR.
The power transformer requirement according to schematic:
Primary: 110VAC or 120VAC
Secondary B+: 391-0-391, 100mA(minimum)
Secondary 5U4 filament: 5V/3A
Secondary 6L6 & 6J7 filaments: 6.3V/3A(minimum)
If the choke's current rating is 130mA then the HV secondary should be similar.
I believe Hammond model 374X should be fine with the following specs:
750VCT/127mA, 5VCT/3A, 6.3VCT/5A
Hammond model 375X at higher power will also work with following specs:
800VCT/155mA, 5VCT/3A, 6.3VCT/5A
You can always tune the value of C4 (4μf stock) to target 384VDC B+ after the choke and then the rest will fall into place.
Cosmetically, the above transformers have end bells but I believe Hammond also made potted versions of the same irons, if you want to match the WE look. Check with manufacture or dealer for availability.
As for the output transformer, the Peerless 16309 or 16458 in the Heathkit W5 with 10K primary will work fine. I think the W5 is probably good for conversion, except you have to lower the B+ voltage.
The Heathkit W4 is indeed a good candidate for converting into the 124 circuit. And it makes sense since it uses all octal tubes and the power transformer and choke will be very close to spec of the 124. I don't know the impedance of the stock Stancor 51-17 output transformer though. Anybody knows the primary impedance? If it's close to 10K then you are better off acquiring a pair of W4's to start the project in terms of ease. A pair of them are cheaper than buying all new parts! Scratch building is a different story, of course. And I understand the joy of it!
The schematic of the Heathkit W4 shows specs of the Stancor 54-29 power transformer:
380-0-380/130mA, 5V/3A, 6.3V/4A
It's almost perfect for 124 conversion!
An externally hosted image should be here but it was not working when we last tested it.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
The L1, 221G choke drops 19v via 99mA so its DCR is 192Ω and
the one that's close in the Hammond catalog is model 159P and its spec is 5H, 125mA, 155Ω DCR.
The power transformer requirement according to schematic:
Primary: 110VAC or 120VAC
Secondary B+: 391-0-391, 100mA(minimum)
Secondary 5U4 filament: 5V/3A
Secondary 6L6 & 6J7 filaments: 6.3V/3A(minimum)
If the choke's current rating is 130mA then the HV secondary should be similar.
I believe Hammond model 374X should be fine with the following specs:
750VCT/127mA, 5VCT/3A, 6.3VCT/5A
Hammond model 375X at higher power will also work with following specs:
800VCT/155mA, 5VCT/3A, 6.3VCT/5A
You can always tune the value of C4 (4μf stock) to target 384VDC B+ after the choke and then the rest will fall into place.
Cosmetically, the above transformers have end bells but I believe Hammond also made potted versions of the same irons, if you want to match the WE look. Check with manufacture or dealer for availability.
As for the output transformer, the Peerless 16309 or 16458 in the Heathkit W5 with 10K primary will work fine. I think the W5 is probably good for conversion, except you have to lower the B+ voltage.
The Heathkit W4 is indeed a good candidate for converting into the 124 circuit. And it makes sense since it uses all octal tubes and the power transformer and choke will be very close to spec of the 124. I don't know the impedance of the stock Stancor 51-17 output transformer though. Anybody knows the primary impedance? If it's close to 10K then you are better off acquiring a pair of W4's to start the project in terms of ease. A pair of them are cheaper than buying all new parts! Scratch building is a different story, of course. And I understand the joy of it!
The schematic of the Heathkit W4 shows specs of the Stancor 54-29 power transformer:
380-0-380/130mA, 5V/3A, 6.3V/4A
It's almost perfect for 124 conversion!
In the 124 that I tested, it does achieve the 384VDC B+. The C4 size of 4µf is crucial. In a DIY amp, you can always tune the size to get the targeted voltage.
The original 124's I checked, all early versions that belong to a friend, are surprisingly quiet, no hum no buzz even on 100dB horn speakers, so I agree that high inductance maybe the reason, consider all the filters caps are rather modest size in value. I never got the chance to measure the inductance, unfortunately.
The 124 is a pleasant sounding amp. And like most PP amps with paraphase inverter, it has a very pleasing harmonic richness to it and "bloom" and very transparent at the top and no audible HF roll off. Euphonic distortion or not, I frankly don't care. Is it the best sounding PP 6L6 amp I've heard? No.
More Transformer questions:
Wow- This is great info .. Thank you for all this. I still have a couple more questions I spoke with Jack Elliano at Electra print transformer about some output transformers =. He mentions only being able to make a 10K ohm out put transformer rated for 100ma of current . Is this cutting it too close? I would like to hook my version of the 124 up for 20 watts so that would me a higher b+ voltage ( it says 426 v. on the schematic) . Is this going to generate too much current for Jack's 100ma rated output trans.? I already asked this question is some form but I still am not confident enough to order a transformer from him. People are responding to the 391 B+ hook up in the schematic which supposedly generates 12 watts.
Also, I have had good luck with Hammond power transformers. Someone here suggested I use the EDcor line, stating that they are much quieter. How do you feel about their products?
Wow- This is great info .. Thank you for all this. I still have a couple more questions I spoke with Jack Elliano at Electra print transformer about some output transformers =. He mentions only being able to make a 10K ohm out put transformer rated for 100ma of current . Is this cutting it too close? I would like to hook my version of the 124 up for 20 watts so that would me a higher b+ voltage ( it says 426 v. on the schematic) . Is this going to generate too much current for Jack's 100ma rated output trans.? I already asked this question is some form but I still am not confident enough to order a transformer from him. People are responding to the 391 B+ hook up in the schematic which supposedly generates 12 watts.
Also, I have had good luck with Hammond power transformers. Someone here suggested I use the EDcor line, stating that they are much quieter. How do you feel about their products?
The Hammond 200 series run at very high induction and are prone to make noise if the line voltage is even slightly higher than rated - they are also rated 60Hz only. But the 300 series with 50/60Hz rating have more margin, at least if they are used at 60Hz.
Presumably this is because too many amateurs are cheapskates! :^) that' a funny, you may laugh now...
Presumably this is because too many amateurs are cheapskates! :^) that' a funny, you may laugh now...
From AA (dgillispie): "The primary impedance is 10K, with the screen taps located at 50% of the winding. It is a 20 watt transformer, so max current will be in the 150 ma range."
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.