Dynaco A470 O/T

[Hennie]

Hi there, I recently got hold of a Dynaco A470 ultralinear output transformer. The rating shows 35w/70w which is the correct rating?If I should use it on an ac30 clone how high can I push the Plate voltages on the 4 6BQ5's. Please help: confused:

[Rob Mercure]

The seventy watt rating must be "peak" with the 35 being continuous - 70W out of four 6BQ5s would melt 'em <grin>.

How high does the AC30 run the plates? You should be able to use to use the same voltage - it's the plate dissipation that you've got to watch. 'Specially as this is a "quasi" Class A design which will dissipate more heat than a "normal" Class AB1.

Rob

[Hennie]

Thanks Rob, Im still planning to build the Ac30. Should I connect the tranny normally or should I use the ultralinear connection?My power transformer gives out 135v I thought a voltage doubler should work(multiplied by 2.6) =350v

[Tom Phillips]

From my old Dynaco catalog the ratings mean:
70 Watts "Undistorted power 30 cps to 15kc"
35 Watts "Undistorted power 20 cps to 20kc"
For those who are wondering cps = cycles per second = Hz in modern speak.
Regards,
Tom

[bob p]

Hi there, I recently got hold of a Dynaco A470 ultralinear output transformer. The rating shows 35w/70w which is the correct rating?If I should use it on an ac30 clone how high can I push the Plate voltages on the 4 6BQ5's. Please help: confused:

the Dynaco A470 OT was used in the Dynaco Stereo 70 HiFi amplifier. The ST70 used a pair of EL34/6CA7, and the amp was spec'd to deliver 35W continuous, 80W peak per channel. Looking at the assembly manual that I found online, the freq response rating for the amp was 10 cps to 40 kc +/- 0.5 dB, and the power response of the amp was rated at 20 cps - 20kc +/- 1 dB at 35W output with less than 1% distortion. Pretty good specs for an OT, and way better than what you'd ever need for a guitar amp.

As it turns out, the ST70 is THE world's most popular tube HiFi restoration project. There are a great many Dynacos out there, and the vast number of them are in need of some repair. Many of them need OTs.

Thinking about the great number of people who restore old Dynacos, people are always in search of original Dynaco A470 output transformers. Original A470 OT are hard to come by, and most people restoring an ST70 are forced to use a repro OT because originals aren't available. IIRC, repro OTs go for about $100, and originals go for considerably more.

In all likelihood, you would probably be money ahead by selling that original Dynaco A470 to someone who needs it for a restoration project, and using the money to buy the right OT for an AC30 build. When the smoke clears you'll probably have a reasonable amount of money left over.

[bob p]

From my old Dynaco catalog ...

Tom, had you ever considered scanning that old Dynaco catalog and putting it online? I for one would like to see it.

[Tom Phillips]

Tom, had you ever considered scanning that old Dynaco catalog and putting it online? I for one would like to see it.

Sure - I'll put that on my to do list. The page I found was only a partial copy but I have an original catalog here somewhere. I built a few amps with the Dynaco A-451. 24 pounds of great OT!
Regards,
Tom