My next project... Tucker 45 PF monos

[jrebman]

I'm not sure if theis the right place to post this, but here goes anyway.  I'm seriously onsidering building myself a pair of John Tucker's direct-coupled, shunt-regulated, parafeed 45 amps that were published in Valve in 1997/98 or thereabouts.

Was wondering if anybody has built/heard these, and what their impressions arre, especially how quiet they are.  Any changes that you would or did make -- such as using the current BH C4S boards, etc.?  Any changes to the driver tube?  Maybe the new soft-start boards with the 5670?

I'll have to get the schematic translated for me so I can look at this for myself and figure out what's going on, but any feedback from experienced builders/users would be great.

Thanks,

Jim

 

[xcortes]

I built them and they're great amps. As per PJs suggestion I used only one section of the driver tube (instead of both in parallel as in the original article) with a simple 6mA C4S. I guess a SR driver would work great.

They're simple so it's a great project to do your first "scratch build".

I don't think that the PGP 8.1s are available anymore.

 

[jrebman]

Thanks, Xavier.

No worries on the power tx, I can and will have custom ones made, and will probably use separate filament transformers.

-- Jim

 

[Paul Joppa]

Found it! VALVE, volume 4 number 10, October 1997, page 11. It does not incorporate a shunt regulator - that was a later development. (And be aware that usually we refer to a shunt regulated driver stage, but have done a small number of amps with the whole amp shunt regulated - the nomenclature does not do a good job of distinguishing between them.)

It should be a great project, simple but sophisticated.

There are several small changes I would suggest, based on what we've learned over the last 13 years. This circuit, along with the Bottlehead Afterglow (originally Tucker's design) and the custom-only Excite which IIRC existed in both 45 and 2A3 forms, became the starting points for the Paraglow and eventually the 2A3 Paramount - with numerous changes along the way. So we have a variety of experiences with it.

The most critical thing is the power supply, whose voltage must be tightly controlled. In the original, the voltage at the 45 plate was 400 volts, plus 20 volts for the drop across the plate choke - power supply 420 volts. Different power transformers with the same nominal volts can give wildly different output voltages; I have seen over 500 volts from power transformers with the same 350-0-350v nominal rating. This places the power supply capacitors, the current source, and even the 45 at risk of premature failure. (Also there are some typos - the 1/4 watt bleeders will dissipate 2/3 watt; I would not use anything less than a 2-watt rating!)

If you would like some detailed notes on my thoughts, I'd be happy to write up something - ping me through the forum if interested.

 

[xcortes]

Here's the link to the article:

http://www.positive-feedback.com/Issue1/single.htm