Output Transformer Question

[dicranurus]

I am building a pair of monoblocks amplifiers. Each amp uses 4 KT88 tubes in parrelel. The design calls for 100 W ultralinear output transformers with input impeadance of 3200 ohms. I have available some Edcore transformers, but they have input impeadance of 2500 ohms. Will these work and what effect will it have on sound quality? thanks for your help.

 

[azazello]

If You mean SE, Ra each tube is about 2-2.2 kohm, if I'm not wrong. 4 in parallel have 500-600 ohm. IMO, 2.5 kohm is suitable, like 3.2 kohm. Probably You will not sense the difference. /With 2.5 - more power, with 3.2 - more bass...but KT88 has great bass/.

 

[gingertube]

In the past I've used Hammond 1650T and Plitron VDV2100 for parallel push pull Ultralinear KT88. Both of these are Raa approx 2K and worked well with a B+ of just over +500V.

An Raa of 2500 Ohms will be fine - proceed with confidence.

In general, a higher Raa will give less power but also less distortion but the difference between 3200 and 2500 Ohms will be marginal.

Cheers,
Ian

 

[dicranurus]

Thanks all. I very much appreciate your input.

 

[gingertube]

At the B+ of just over +500V and the 2K (actually 1900 Ohms) Raa Hammond 1650T I got 122W at the onset of clipping and 138W in heavy overdrive.
I would probably do things a little differently today but I have attached some details of what I did "back then" for your possible interest.

Cheers,
Ian

 

[Xpersephone2]

With 4 KT120 in ultralinear PPP a Lundahl LL1693 gives 155W at the beginning of clipping. B+ is 495V regulated. KT88 would not be very different.

 

[dicranurus]

This is great stuff thanks to all. My B+ is 465V. We'll see when kind of Power I get.

Ian
I love your bias circuit. I may adapt it my my set up. Thanks

Mike