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In Reply to: RE: Help needed: 4uF PIO capacitor (Hunts) sought, or PIO replacements? posted by jusbe on February 26, 2015 at 20:00:26
on ebay UK, If I were you, I'll get the original. That kind of cap is really tough, are you sure the problem is due to that 4uf cap?
Follow Ups:
suggested that the values were different enough to cause some issues of balance between channels. Not sure I understand what he means. I will look out for them and see if I can find a closely matched pair.
He's doing some generally repair work on the internal out-of-spec caps elsewhere in the circuit with modern equivalents for the time being. This will allow me to assemble NOS replacements for the internal pieces which are more in keeping with the vintage.
All of this triggered, apparently by two faulty RFT EL34s which permitted runaway voltages to creep into the circuit.
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
Big J
When you say runaway voltages,are the tubes turning red or orange on the plates? Also,you may have to change the tubes if they were the ones giving you problems but if you don't at least change C7 and C8,you will have problems..You can use the Russian K40Y-9 pio caps which I use in everything and personally,they are more reliable than the Jensens because they are also hermetically sealed and don't leak like Jensens would.
You can also use a film caps for C7 and C8 like Steve suggested.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
I wish I knew more about amp design than I do. Noted your K40Y-9 recommendation.
I've supplied my KT77s as replacements, since they're reissues and more are readily available.
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
J
This is a very nice amp and it's very simple and easy to fix with just a DVM. There is no rocket science here.You change the original coupling capacitors out along with the any other capacitors on that board like the small electrolytics..Nichicon muses are wonderful for that but keep in mind you should check the resistors by lifting one side and measuring them with your ohmmeter.Many you can measure right in circuit without disconnecting them and they only need to read within 10% of the value if there is a silver colored band on them and within 5% if there is a gold colored band on them.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
when I get it back after this repair is exactly this. Systematically go through the amp with some basic tools, measure and learn. Since I intend to keep these amps, it would pay to become very familiar with them. Then, perhaps, I can effect my own maintenance and repair myself in the future.
Thanks for your advice, Michael.
Justin.
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
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