OT question - will it work?

atmars · 26th November 2008, 05:45 AM

Hi,

i got a hold of an amp chassis that had basically the same tube compliment as a 5E3 except it is a transformerless amp with 25L6s as power tubes. i also had a power transformer that would run a 5E3, so thinking myself quite clever, I set about rebuilding a deluxe into the chassis and got rid of the old tubes. Then, after reading Jack Darr I realized I probably made a big mistake. Will the OT work? Darr was talking about replacing OTs and mentioned matching load resistances and plate to plate load impedance and a realized this material is out of my depth. i can't seem to find the same kind of data on the 25l6s that are available for the 6v6s so I can't even do a side by side comparison. Can some one lend a hand here?

If I have to dump the old OT is there anything I might be able to find on ebay that will get the job done. I see a lot of pro jr. type OTs out (although i believe they run el84s) , or should I just buy a tweed deluxe replacement?

Thanks

atmars · 27th November 2008, 01:35 PM

Maybe I need to rephrase this question -

I realize that the OT will "work" but how does one calculate how it will work optimally?

What data does one use and how is it use to match on output transformer and a set of (or one) power tube?
I found this link showing how to test an unknown OT

http://www.diyguitarist.com/GuitarAm...lectedLoad.htm

But it does not specify how this test is done for a push pull OT.

Any insight would be greatly appreciated.

Tom Bavis · 27th November 2008, 02:54 PM

The 25L6s would use a 4KCT output transformer, and 6V6s would like about 8KCT. The 6V equivalent of the 25L6 is the 6W6 - but it probably isn't worth the trouble to get a low-voltage transformer for those (and end up with half the power of 6V6s...).

You can TRY a speaker load impedance of double the original, which will present 8K to the output tubes but you'll lose an octave from the low frequency response. You may have4 to bite the bullet and get a proper 6V6 transformer.

atmars · 28th November 2008, 01:25 AM

Thanks - I'm still waiting on parts so I will be able to do the "ear" test. If it sucks I'll try some thing else. Will a recycled blues jr. OT get the job done?

26th November 2008, 05:45 AM	#1
atmars diyAudio Member Join Date: May 2008	OT question - will it work? Hi, i got a hold of an amp chassis that had basically the same tube compliment as a 5E3 except it is a transformerless amp with 25L6s as power tubes. i also had a power transformer that would run a 5E3, so thinking myself quite clever, I set about rebuilding a deluxe into the chassis and got rid of the old tubes. Then, after reading Jack Darr I realized I probably made a big mistake. Will the OT work? Darr was talking about replacing OTs and mentioned matching load resistances and plate to plate load impedance and a realized this material is out of my depth. i can't seem to find the same kind of data on the 25l6s that are available for the 6v6s so I can't even do a side by side comparison. Can some one lend a hand here? If I have to dump the old OT is there anything I might be able to find on ebay that will get the job done. I see a lot of pro jr. type OTs out (although i believe they run el84s) , or should I just buy a tweed deluxe replacement? Thanks

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27th November 2008, 01:35 PM	#2
atmars diyAudio Member Join Date: May 2008	Maybe I need to rephrase this question - I realize that the OT will "work" but how does one calculate how it will work optimally? What data does one use and how is it use to match on output transformer and a set of (or one) power tube? I found this link showing how to test an unknown OT http://www.diyguitarist.com/GuitarAm...lectedLoad.htm But it does not specify how this test is done for a push pull OT. Any insight would be greatly appreciated.

27th November 2008, 02:54 PM	#3
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	The 25L6s would use a 4KCT output transformer, and 6V6s would like about 8KCT. The 6V equivalent of the 25L6 is the 6W6 - but it probably isn't worth the trouble to get a low-voltage transformer for those (and end up with half the power of 6V6s...). You can TRY a speaker load impedance of double the original, which will present 8K to the output tubes but you'll lose an octave from the low frequency response. You may have4 to bite the bullet and get a proper 6V6 transformer.

28th November 2008, 01:25 AM	#4
atmars diyAudio Member Join Date: May 2008	Thanks - I'm still waiting on parts so I will be able to do the "ear" test. If it sucks I'll try some thing else. Will a recycled blues jr. OT get the job done?