Hiwatt custom tranformer 70v bias question

[Brianvcskin]

Bias voltage mod

Am building a hiwatt DR103 clone 90% complete but am looking getting a transformer built with 70v bias tap. Stock is 50v but hiwatt always run hot(not enough bias voltage) wondering if this would work. And what I should change the bias resistors to. Here is the bias circuit I'm looking at using for a basis the Dr103 with one pot. Thanks people hope you can help.

 

[Brianvcskin]

Bias voltage mod hiwatt

Am 90% complete with my hiwatt DR103 (4xel34) clone but want to do improve the anemic bias circuit. Haven't purchased a PT yet but am looking at betting a custom toroidal build with a 70v bias tap as the stock 50v is not enough they run hot usually around 38v. There is a mid circuit with one pot I was going to use. Need to know if a 70v tap will work if so what value should my resistors be. Thanks in advance.

 

[Brianvcskin]

Am 90% complete with my hiwatt DR103 (4xel34) clone but want to do improve the anemic bias circuit. Haven't purchased a PT yet but am looking at betting a custom toroidal build with a 70v bias tap as the stock 50v is not enough they run hot usually around 38v. There is a mid circuit with one pot I was going to use. Need to know if a 70v tap will work if so what value should my resistors be. Thanks in advance.

 

[JonSnell Electronic]

Reduce the load resistor and the bias voltage will increase. 50V AC is ample to produce up to 60Vvolts of negative DC. EL34 only needs 42Volts to run cool and sound like a Marshall, in a HiWatt.

 

[artosalo]

...am looking at betting a custom toroidal build with a 70v bias tap as the stock 50v is not enough they run hot usually around 38v.

The current of a bias ciruit is very low. Therefore simple voltage doubler works fine with original power transformer.
You do not need to have a custom transformer just for bias.

 

[Brianvcskin]

The current of a bias ciruit is very low. Therefore simple voltage doubler works fine with original power transformer.
You do not need to have a custom transformer just for bias.

For the cost of shipping a mercury magnetics(120v primary only I believe) or Hammond or partridge clone I can have a toroidal built to my spec cheaper . This is why I was looking at this route . Or should I just get one built with 50v and use the doubler circuit?

 

[AndrewT]

http://www.diyaudio.com/forums/power-supplies/288355-bias-voltage-mod.html#post4646703

is this the same?

 

[Mooly]

Brian, I have merged your two threads. Please only start one thread per topic.

 

[artosalo]

50 Vac is fully sufficient to get 60 Vdc for bias purposes.
But if make a custom design transformer, then you can order 70 V bias secondary, if you like it more.

 

[Cal Weldon]

3rd thread merged.
Brian please read the rules before posting again.

 

[Brianvcskin]

3rd thread merged.
Brian please read the rules before posting again.

Apologies didn't think the first one posted so I tried again didn't realise a moderator had to confirm it.

 

[mark31385]

I would have said to have a word with Rick from HiWatt or even Jeff at Matamp. But they are against clones. Maybe a phone call to either would tell you why.