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Hi folks!

I'm a day or two away from completing my ST-70 clone using all-new parts from Triode/Dynakits except for a pair of original A470 output transformers (which interestingly appear to be a mixture of cloth covered for some wires, and PVC only for others!!!).

As I am using the beefy 240V PA-521-S power transformer I am thinking that an inrush limiter might be necessary, especially as I want to protect my Mullard GZ34s! Would the CL80 which people mention here be suitable for the 240V transformer I have, or would I need something else?

If someone could provide me with one (if it's suitable) I'd gladly PayPal you the amount for a couple beers in return

Cheers,

- Johm

Go to the data-sheets for the in-rush limiter, and pick one that fits you spec current draw. They are sized by current draw, not voltage.

mugsy wrote:Hi folks!

I'm a day or two away from completing my ST-70 clone using all-new parts from Triode/Dynakits except for a pair of original A470 output transformers (which interestingly appear to be a mixture of cloth covered for some wires, and PVC only for others!!!).

As I am using the beefy 240V PA-521-S power transformer I am thinking that an inrush limiter might be necessary, especially as I want to protect my Mullard GZ34s! Would the CL80 which people mention here be suitable for the 240V transformer I have, or would I need something else?

If someone could provide me with one (if it's suitable) I'd gladly PayPal you the amount for a couple beers in return

Cheers,

- Johm

IMHO a current in-rush limiter is not really necessary with any amp with a GZ34 rectifier. A GZ34 rectifier is indirectly heated and takes maybe 10 or 15 seconds before it can apply high voltage. By that time the tube heaters have warmed up a little. Even some solid state rectifiers that plug into the GZ34 tube socket, like the WZ-68 Weber Copper Cap rectifier, have a short built in time delay (2 or 3 seconds) built in. The Weber Cap, by the way, gives higher B+ voltages than any tube rectifier I have tried (Mullards included) in any ST-70 I have used. The Weber also will not sag the B+ voltage down at high current demands when the amp is playing loudly. I can notice immediately more low end sock with the Weber at high volumes on the 70

On an amp with a solid state rectifier which will apply the high voltage almost instantly an in-rush limiter might be a good idea. The Dynaco ST-35 is a good example. I use one on my ST-35.

Bob Latino

Many thanks Bob - that's put my mind at rest. I'll see how I go without one.

Thanks for the replies all,

- John