Hello,
I have to obtain the power and output transformers for what will be my first amp project, built from a partial kit. I'm running into difficulty in locating transformers that match exactly what I need.
The amp is described as a push-pull, but the only output transformer available here in the states I've seen so far is described as being used with single-ended designs. I've attached the schematic from the E-Bay listing. The transformer I think may work is an Edcor GXSE15-8-3.5K. The connections look correct, and the primary winding resistance looks correct, though it's described as being used for single ended designs. The closes push-pull design output transformer Edcor lists is a GXPP15-8-5K-but the primary resistance is higher and it has additional leads on the primary side I wouldn't know what to do with. I'm thinking the schematic doesn't follow every neat and tidy convention when it comes to tube amp design.
Regarding the power transformer, the recommended spec is as follows (secondary side): 1X 280-0-280@100mA, 2X 3.15-0-3.15@1.5A, 1X 5V@ 3.5A, and 2X 2.5V@5.0A. Straight off it looks like the 2.5V (filament) supply is usuall supplied by a stand alone transformer, but the others (beyond the 280V supply, I'm not even sure what they're for!) are often packaged in the same transformer. My most fundamental question is how sensitive are the tubes to the specific voltage and current they receive? Would a 330-0-330 work ok? If the lower voltage components see a supply with greater current capability, is there a risk of burning anything out? I was always given to understand that no electrical component will use more current than it needs, however in playing around with some small stuff on PCBs recently I've learned that there are indeed 'dumb' components out there which if you do not provide current limiting resistance, will self destruct. I read something to this effect regarding the tube filament supply.
Thank you very much for your suggestions,
Rick
I have to obtain the power and output transformers for what will be my first amp project, built from a partial kit. I'm running into difficulty in locating transformers that match exactly what I need.
The amp is described as a push-pull, but the only output transformer available here in the states I've seen so far is described as being used with single-ended designs. I've attached the schematic from the E-Bay listing. The transformer I think may work is an Edcor GXSE15-8-3.5K. The connections look correct, and the primary winding resistance looks correct, though it's described as being used for single ended designs. The closes push-pull design output transformer Edcor lists is a GXPP15-8-5K-but the primary resistance is higher and it has additional leads on the primary side I wouldn't know what to do with. I'm thinking the schematic doesn't follow every neat and tidy convention when it comes to tube amp design.
Regarding the power transformer, the recommended spec is as follows (secondary side): 1X 280-0-280@100mA, 2X 3.15-0-3.15@1.5A, 1X 5V@ 3.5A, and 2X 2.5V@5.0A. Straight off it looks like the 2.5V (filament) supply is usuall supplied by a stand alone transformer, but the others (beyond the 280V supply, I'm not even sure what they're for!) are often packaged in the same transformer. My most fundamental question is how sensitive are the tubes to the specific voltage and current they receive? Would a 330-0-330 work ok? If the lower voltage components see a supply with greater current capability, is there a risk of burning anything out? I was always given to understand that no electrical component will use more current than it needs, however in playing around with some small stuff on PCBs recently I've learned that there are indeed 'dumb' components out there which if you do not provide current limiting resistance, will self destruct. I read something to this effect regarding the tube filament supply.
Thank you very much for your suggestions,
Rick
Push-pull and single-ended OPT are quite different. You need the right one to match your circuit. The exact impedance is less important.
Small variations in supply voltage do not matter. Going from 280 to 330 is almost 20% so too big a jump unless you can redesign the circuit to suit.
Small variations in supply voltage do not matter. Going from 280 to 330 is almost 20% so too big a jump unless you can redesign the circuit to suit.
Maybe just find some iron from an older amplifier and learn to build something around that.
A "tube amp kit" with no transformers and tubes is likely just a PCB with a few components on it?
A "tube amp kit" with no transformers and tubes is likely just a PCB with a few components on it?
Edcor is known for decent entry level SE OPT's, but if you can afford it & you want PP there are sonically better ones out there for a bit more money (more interleaving which takes time so more $) starting with the Dynaco EL84/6BQ5 PP Z-565 clones used in the SCA/ST-35 amps from Triode Electronics, Magnequest and more recently dynakit parts. Heyboer can also wind some nice OPT's Remember the OPT (output transformer) is the heart of a tube amp sonically.
Here is the transformer company list on this site.
TransformerSuppliers - diyAudio
Here is the transformer company list on this site.
TransformerSuppliers - diyAudio
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Here's some good proven info with some of it for buying & repairing good vintage equipment & diy etc. which may help you I've posted on another site under " Looking for Dynaco Alternatives" as some of the ebay PCB's may not be so good:
Assuming you want PP (Push Pull) Vintage integrated Eico, Heathkit, Fisher, Scott, and Sherwood with EL84/6BQ5/7189 for 15-20W/CH if you have the right efficient speakers comes to mind. Some Pilot amps and pre amps would be great also.
If you want about 35W/CH you will find some from the above companies with EL34/6CA7 and 7591/7868 tubes.
Sometimes receivers are more affordable and easier to find also.
Just don't plug in an old unit as the old caps may not be up to it causing a loss of a transformer or two.
Using a variac with a dim bulb tester is the best way to test an old unit before recapping which must be done for reliability and so you don't risk any of the transformers.
Here are some rebuilding tips You can learn how to repair & troubleshoot by diy if your careful with unplugging it when working on it. Just make sure PS (power supply) caps are discharged with say a 100K to 200K resistor soldered to a piece of wire.
A good soldering station is well worth buying for under $100 like a 51 series Weller and Haako 888 which both have adjustable temp. They make soldering easy! A good solder sucker is good to have also.
Check out the tubelab.com site for good soldering instructions also.
Here is a general rebuilding guide:
Jim of Jim McShane Tubes will make a kit of parts up for you to rebuild it if you contact him. He is a great guy to deal with and is well known for his HK Citation kits & well tested tubes.
(1) Old tube amps shouldn't just be plugged in as old capacitors can take out Transformers (s) and Tubes.
(2) Always have a load on the speaker outputs (25W + 16 ohm resistors if testing) as you can take out Output Transformers
(3) Always Wait 5 minutes (or more till tubes are cold) after shutting amp off before powering up again as the Tubes and if not lucky Transformers can suffer fatal damage. Caps can also be damaged. Basically the tubes are still conducting (regulate voltage) when warm and if started up again they can conduct at the wrong time or way.
Anyway if you want to power it up safely also clean all tube sockets and pins for best results.
You need a dim bulb tester in line with a variac to do it safely. The bulb is to help warn of a short condition.
You can get away with just light bulbs, but the variac is great to have!
Before recapping (Power Supply including can caps, bias caps , & coupling caps) and checking resistors take Lots of Detailed Pictures.
You can do it, by replacing one or two caps at a time, then checking for correct operation.
Can caps can be unhooked and left for looks with new caps strapped under chassis (this is a lot cheaper also) Jim may set you up with modern big caps clamped in place of the old ones. Some people like to re stuff the can caps with small skinny ones , but guys like Jim say the modern big caps(big round caps in the same diameter as the old can ones) like the JJ's, Panasonic etc work better sonically.
Heyseed hamfest is supposed to make really nice reproductions of the old can caps.
Resistors usually go high in value so they can be checked in circuit.
Pot's and switches should be cleaned with the right cleaners also as they can cause many problems.
Any selenium rectifiers that are usually used in fixed bias supplies usually should also be replaced with modern SS diodes.
Just start studying the schematics so you can learn to trace the circuit wiring.
A final and maybe the best sonically is diy an amp as the Output Transformers are the heart of the amp for sonics and you can pick a design that dispenses with controls in the signal path you don't need. There have been nice designs on this form in recent months along with other forms like diyaudio through the years.
Many of the upgrade boards for Dynaco's use the popular PP Mullard circuit now days so the only really Dynaco part left affecting the sonics of an amp are the Dynaco OPT's (output Transformers)
The Williamson or derivative of it is another circuit to look at also. On the lower power amps EL84/6BQ5/ 6V6 many like the floating Paraphase circuit. It was actually used on many vintage amps mentioned above.
If you don't want to P2P, a PCB from the Dynaco vendors and others are a simpler faster answer.
Check out classicvalvedesign, diytube, tubelab (they have SE /SET PCB's if you want to try that also) , Pete Millet (lot's of info from books etc. to download and read on his site also) , triode electronics, and tubes4hifi.
K & K Audio also has a unique design running in class A1 PP (Giving affordable SE sonic advantages with the power of PP ) with input transformers that allows you to only basically keep the Dynaco look as they offer Lundahl OPT's as an upgrade.
Assuming you want PP (Push Pull) Vintage integrated Eico, Heathkit, Fisher, Scott, and Sherwood with EL84/6BQ5/7189 for 15-20W/CH if you have the right efficient speakers comes to mind. Some Pilot amps and pre amps would be great also.
If you want about 35W/CH you will find some from the above companies with EL34/6CA7 and 7591/7868 tubes.
Sometimes receivers are more affordable and easier to find also.
Just don't plug in an old unit as the old caps may not be up to it causing a loss of a transformer or two.
Using a variac with a dim bulb tester is the best way to test an old unit before recapping which must be done for reliability and so you don't risk any of the transformers.
Here are some rebuilding tips You can learn how to repair & troubleshoot by diy if your careful with unplugging it when working on it. Just make sure PS (power supply) caps are discharged with say a 100K to 200K resistor soldered to a piece of wire.
A good soldering station is well worth buying for under $100 like a 51 series Weller and Haako 888 which both have adjustable temp. They make soldering easy! A good solder sucker is good to have also.
Check out the tubelab.com site for good soldering instructions also.
Here is a general rebuilding guide:
Jim of Jim McShane Tubes will make a kit of parts up for you to rebuild it if you contact him. He is a great guy to deal with and is well known for his HK Citation kits & well tested tubes.
(1) Old tube amps shouldn't just be plugged in as old capacitors can take out Transformers (s) and Tubes.
(2) Always have a load on the speaker outputs (25W + 16 ohm resistors if testing) as you can take out Output Transformers
(3) Always Wait 5 minutes (or more till tubes are cold) after shutting amp off before powering up again as the Tubes and if not lucky Transformers can suffer fatal damage. Caps can also be damaged. Basically the tubes are still conducting (regulate voltage) when warm and if started up again they can conduct at the wrong time or way.
Anyway if you want to power it up safely also clean all tube sockets and pins for best results.
You need a dim bulb tester in line with a variac to do it safely. The bulb is to help warn of a short condition.
You can get away with just light bulbs, but the variac is great to have!
Before recapping (Power Supply including can caps, bias caps , & coupling caps) and checking resistors take Lots of Detailed Pictures.
You can do it, by replacing one or two caps at a time, then checking for correct operation.
Can caps can be unhooked and left for looks with new caps strapped under chassis (this is a lot cheaper also) Jim may set you up with modern big caps clamped in place of the old ones. Some people like to re stuff the can caps with small skinny ones , but guys like Jim say the modern big caps(big round caps in the same diameter as the old can ones) like the JJ's, Panasonic etc work better sonically.
Heyseed hamfest is supposed to make really nice reproductions of the old can caps.
Resistors usually go high in value so they can be checked in circuit.
Pot's and switches should be cleaned with the right cleaners also as they can cause many problems.
Any selenium rectifiers that are usually used in fixed bias supplies usually should also be replaced with modern SS diodes.
Just start studying the schematics so you can learn to trace the circuit wiring.
A final and maybe the best sonically is diy an amp as the Output Transformers are the heart of the amp for sonics and you can pick a design that dispenses with controls in the signal path you don't need. There have been nice designs on this form in recent months along with other forms like diyaudio through the years.
Many of the upgrade boards for Dynaco's use the popular PP Mullard circuit now days so the only really Dynaco part left affecting the sonics of an amp are the Dynaco OPT's (output Transformers)
The Williamson or derivative of it is another circuit to look at also. On the lower power amps EL84/6BQ5/ 6V6 many like the floating Paraphase circuit. It was actually used on many vintage amps mentioned above.
If you don't want to P2P, a PCB from the Dynaco vendors and others are a simpler faster answer.
Check out classicvalvedesign, diytube, tubelab (they have SE /SET PCB's if you want to try that also) , Pete Millet (lot's of info from books etc. to download and read on his site also) , triode electronics, and tubes4hifi.
K & K Audio also has a unique design running in class A1 PP (Giving affordable SE sonic advantages with the power of PP ) with input transformers that allows you to only basically keep the Dynaco look as they offer Lundahl OPT's as an upgrade.
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