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Thread: Output transformer question

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    Output transformer question

    I purchased a Bogan 110D audio amplifier from e-bay that I was planning to convert to Bogen-DB-110-Service-Manual (1).pdfguitar use. I have been having lots of issues and decided to scrap the conversion. I was thinking of making a Champ clone and want to make sure the transformers are compatible. The Bogan amp has three 12XA7 preamp, two 6V6 power tubes and a 5Y3 rectifier, same tubes as the Champ, just fewer. The power and output transformers appear to be in good condition, no shorts and impedance match the service manual that I pulled from the internet.

    The power transformer has three sections, 700 volt, 5 volt and 6.3 volt and is listed as David Bogan T362-3. The output transformer has 4, 8 and 16-ohm secondary impedances and 11k primary impedance and is model T2106-1.

    My question is that the current output transformer service two 6V6 tubes (connected to pin 3) and the Champ circuit only has one. I was planning on putting the unused lead to a terminal strip inside the chassis. This may sound like a basic question, but would the unused lead that cause any issues with the transformer operation?

    I have included a copy of the Bogan service manual as an attachment,

    Thanks in advance.

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    Quote Originally Posted by mike60510 View Post
    I purchased a Bogan 110D audio amplifier from e-bay that I was planning to convert to Bogen-DB-110-Service-Manual (1).pdfguitar use. I have been having lots of issues and decided to scrap the conversion. I was thinking of making a Champ clone and want to make sure the transformers are compatible. The Bogan amp has three 12XA7 preamp, two 6V6 power tubes and a 5Y3 rectifier, same tubes as the Champ, just fewer. The power and output transformers appear to be in good condition, no shorts and impedance match the service manual that I pulled from the internet.

    The power transformer has three sections, 700 volt, 5 volt and 6.3 volt and is listed as David Bogan T362-3. The output transformer has 4, 8 and 16-ohm secondary impedances and 11k primary impedance and is model T2106-1.

    My question is that the current output transformer service two 6V6 tubes (connected to pin 3) and the Champ circuit only has one. I was planning on putting the unused lead to a terminal strip inside the chassis. This may sound like a basic question, but would the unused lead that cause any issues with the transformer operation?

    I have included a copy of the Bogan service manual as an attachment,

    Thanks in advance.
    You'll run into more issues with hum and noise with that setup than you would if you get a different output transformer. Single ended amps aren't push-pull, so there is no hum cancellation in the output section and as a result the output transformers for single ended amps are made differently to reduce the hum. Output transformers meant for push-pull will function but there will be more noise and hum than if a single ended transformer is used instead. Also there is a bit of an impedance mismatch if you plan to use that output transformer with a single 6V6.

    You should also note that the power transformer is listed as 700VCT, which means it is 700 volts center tapped. The actual voltage to each power tube is 350 volts, as long as the rectifier tube is connected the same way as it was on this amp. If you tried use a solid state diode bridge for example, then the voltage would be much higher, and would be too high for the 6V6. It would be better if you intend to use that transformer set to make a later tweed Princeton or a tweed Deluxe clone since they are push-pull with a 6V6 pair and the voltages are similar.

    Greg

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    Quote Originally Posted by soundmasterg View Post
    You'll run into more issues with hum and noise with that setup than you would if you get a different output transformer. Single ended amps aren't push-pull, so there is no hum cancellation in the output section and as a result the output transformers for single ended amps are made differently to reduce the hum. Output transformers meant for push-pull will function but there will be more noise and hum than if a single ended transformer is used instead. Also there is a bit of an impedance mismatch if you plan to use that output transformer with a single 6V6.

    You should also note that the power transformer is listed as 700VCT, which means it is 700 volts center tapped. The actual voltage to each power tube is 350 volts, as long as the rectifier tube is connected the same way as it was on this amp. If you tried use a solid state diode bridge for example, then the voltage would be much higher, and would be too high for the 6V6. It would be better if you intend to use that transformer set to make a later tweed Princeton or a tweed Deluxe clone since they are push-pull with a 6V6 pair and the voltages are similar.

    Greg
    I was afraid you someone would tell me that.

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    Supporting Member eschertron's Avatar
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    So make a 2x6V6 Princeton. Or Tweed Deluxe-ish build. You have plenty of options for something that uses the same tube complement as the Bogen. One fewer preamp tube won't make a difference the way one fewer power tube does.

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    I just took a look at the Bogen schem. Did it work before you gutted it? It might have been a decent conversion with just a little effort.

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    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


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    I have not gutted it yet. I replaced all the old caps and rewired the 1st two preamp tubes to resemble a Fender Bassman circuit. I decided not to mess with the phase inverter and the power tube sections. I had sound for about 15 minutes and was very pleased, then the volume dropped, sound got distorted (not the good kind) then no sound. The amp has not been cooperating. The chassis was a bit rusty and I think that the two preamp sockets need to be changed. I may give it one more try before giving up. Thanks for the help

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