DIY Dynaco ST70

[wingking3000]

Hi, All,

I am a newly for tube amplifier. I want to DIY a dynaco ST70 as my tube amp, but using hammond 1645 (30W)

http://www.hammondmfg.com/pdf/5c0051-52.pdf

to replace A470 in output board. I know A470 should be 35W and design for ST70, do anyone advise any problem on this idea? any B+ problem, or damage to the 1645?



Thanks.

[Tom Bavis]

If you have these transformers, you can certainly do it, but don't expect 35W, especially at the frequency extremes. Hammond rates their transformers from 30 Hz to 30 KHz, as I recall, and it will drop off more at 20 Hz. The high end might suffer a little too, as coupling won't be ideal with the 70V secondary taking up winding space. And of course, the feedback compensation components will have to be tweaked with any transformer but an A-470. I'd choose the 1650H or Dynaclone A-470 myself.

On the plus side, if you don't need maximum power, you can run it at a lower voltage and higher current, closer to class A. Most commercial designs have been at the maximum data sheet ratings, because if they were more conservative, a competitor could offer more watts for the same price... We're under no such constraint.

[Bandersnatch]

hey-Hey!!!,
In my experience, the major cost of a DIY effort has been in the time and effort. The parts bill has been trivial by comparison... So I'd recomend upgrading the Iron. Antek toroid for power, and the 5k 1650R Hammond.
cheers,
Douglas