Hello,
Im planning on changing all the resistors in my ST70, i know what the resistance should be but does not know if I should get the 1watt value or 1/2 value or a greater value. Reason I'm doing this is I'm putting new boards and want to be everything up to spec and also because I messed it up. Don't ask me why. Any help is greatly appreciated.
Im planning on changing all the resistors in my ST70, i know what the resistance should be but does not know if I should get the 1watt value or 1/2 value or a greater value. Reason I'm doing this is I'm putting new boards and want to be everything up to spec and also because I messed it up. Don't ask me why. Any help is greatly appreciated.
I'd use the higher rating for the 1k (nfb loop), 6.8k (B+ supply), 10k (bias circuit), 22k (B+ supply), 47k (phase splitter),
270k (pentode plate), 330k (pentode screen). Match the 47k resistors, or use 1% parts.
Also replace the selenium rectifier with a 1N4005 diode. Often the original coupling capacitors become leaky and need replacement.
Might as well install new tube sockets while you're at it.
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So what should be the wattage. 1 or 1/2 or higher.? I need some value because I don't watt to screw it up. Thanks.
The 1 W rating is plenty for the ones on that list. The rest can be 1/2 W.
The 15.6 ohm resistor is a special 3W part, though it's not on the pcb.
If you had some resistors burn up before, that could be due to some other part
that is bad, or a bad connection, or a bad tube.
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If you have the original carbon composition still installed you can go by those as to the size; the small ones, 3/8 inch long and 1/8 inch in diameter are 1/4 watts. I can't remember if the 47Ks are 1 or 2 watts, but it would be best to use 2. 2 watt carbon composition are 11/16 inch long and 5/16 in diameter.
Your small resistors would be best replaced by Yishay/Dale RN60D series. They are only rated for 1/4 watts, but they are 1/2 watt resistors derated for the military.
Also Yishay CMF60 series, they are the same size as the RN60D but rated 1/2 to 1 watt.
And Vishay CCF60 series.
Your small resistors would be best replaced by Yishay/Dale RN60D series. They are only rated for 1/4 watts, but they are 1/2 watt resistors derated for the military.
Also Yishay CMF60 series, they are the same size as the RN60D but rated 1/2 to 1 watt.
And Vishay CCF60 series.
I forgot to mentions, the resistors I'm replacing is not on the pcb board but the ones that are under the chassis.
I use metal film for everything, even the power supply. Just go with the Dale RN65 resistors.
They may be a little longer than the originals, though.
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The 1k grid resistors and the 470k input resistors can be 1/2W, but I'd still use 1 W for the 10k, 6.8k, 22k.
Don't change the 15.6 ohm resistor.
No, the Dale RN65 resistors are excellent, and will work as well as anything else could in that amp.
Where can you find 1/2 watt resistors with the appropriate voltage rating? I have personally only ever seen suitable 1 watt resistors for tube use.
So I recommend that. Much easier to find. And works just fine, obviously.
So I recommend that. Much easier to find. And works just fine, obviously.
I now use the Panasonic ECG which I get from DK -- the 1W devices are the size of a 1/2W carbon comp.
On the Dynaco Tube Audio Forum we have a link below on the parts layout (with a photo) of the original Dynaco PC-3 driver board ...
Dynaco PC-3 board parts layout
Bob Latino
Dynaco PC-3 board parts layout
Bob Latino
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