Hello. I have to questions and thanks in advance. I purchased an old single ended amp (EL84) on eBay and it worked fine aside from the tremolo circuit and it needing a re-cap job.....volume fluctuations, excess noise, etc.
Question 1:
The recap job calls for 3 20uf cap in a single can but I was unable to find such a cap. I was able to get a JJ cap that has 3 20uf and a single 40uf. I was wondering if I could use the 40uf for some additional filtering? If so how would i use it.
I attached a part of the schematic for your review.
Tremolo:
I have a few of these old Japanese amps and the none of the tremolo circuits work. Where do i begin to trouble shoot the problems? I have no idea how these circuits work.
Single ended amp Filtering and Tremelo Questions
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Single ended amp Filtering and Tremelo Questions
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eniam rognab
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Stevem
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Re: Single ended amp Filtering and Tremelo Questions
Antique electronics supply carrys a 20/20/20/20 475 volt can cap.
parrallel two of the 20s to feed the second node which should be the output tube screen supply.
If this amp is like all the Jap univox /Lafayette amps of the mid 60s than all the caps are oil types that go bad, but sound killer until they do.
Replacing c14, c15 and c16 should get the tremolo back up and running, but if I am right about the oil cap thing, than at some point plan on changing them all out.
also make sure you do not need a foot switch to close the circuit to get the tremolo going as I did not look at the schematic.
Good luck to ya!
Oh by the way, if you need help I work at ALTO MUSIC in your neck of the woods.
parrallel two of the 20s to feed the second node which should be the output tube screen supply.
If this amp is like all the Jap univox /Lafayette amps of the mid 60s than all the caps are oil types that go bad, but sound killer until they do.
Replacing c14, c15 and c16 should get the tremolo back up and running, but if I am right about the oil cap thing, than at some point plan on changing them all out.
also make sure you do not need a foot switch to close the circuit to get the tremolo going as I did not look at the schematic.
Good luck to ya!
Oh by the way, if you need help I work at ALTO MUSIC in your neck of the woods.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Single ended amp Filtering and Tremelo Questions
Ha! Yes did not even see that. I was confused as it was a circuit board and the other 2 20uf caps were on the other side of board, I really hate following traces. Now all i need is to use the jj can cap and run wire to the circuit board. That was very silly of me. To get the 40uf they ran to 20uf in series....I fished old can out of garbage.
Re: Single ended amp Filtering and Tremelo Questions
Steven.... Hey Alto is a great store! The prices are better then what you can find online. If you work in the Rockland store we definitely talked before.
Re: Single ended amp Filtering and Tremelo Questions
With the tremolo, the first thing to try is a change of trem oscillator tube.
If that doesn't work, then you need to look at the power supply (including filter caps), heater circuit, and the LFO circuit R/C network and how the LFO couples to the signal path (i.e.; such as whether it uses a roach/opto-isolator if it has one, or whether it wiggles the bias on one or more signal stages etc)
If that doesn't work, then you need to look at the power supply (including filter caps), heater circuit, and the LFO circuit R/C network and how the LFO couples to the signal path (i.e.; such as whether it uses a roach/opto-isolator if it has one, or whether it wiggles the bias on one or more signal stages etc)
He who dies with the most tubes... wins
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Stevem
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Re: Single ended amp Filtering and Tremelo Questions
Note that caps in serise halve the valve, not double it.
to get 40 uf from two 20 uf caps they must be in parrallel.
I work over in the Middletown store doing repairs and QC on there line of mics and 500 serise modules.
to get 40 uf from two 20 uf caps they must be in parrallel.
I work over in the Middletown store doing repairs and QC on there line of mics and 500 serise modules.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!