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In Reply to: RE: Friend's Jolida 302B blowing fuses....why do they use fast blo fuses in this thing?!? posted by Michael Samra on January 12, 2017 at 15:22:08
Oops!
You are right! I shouldn't have stated that it was McShaned! Ok - he recommended and sent parts for this amp (made it even better!)
The amp is at the shop still because the volume pot and the selector switch was dirty (Jim recommended bypassing the balance control so that isn't in the circuit anymore)..
I can't take pics because of that fact. It's just that i brought this up here because I am head scratching about this one. They had it running for about 6 hours and tested it. Your suggestion that it was perhaps best to use a slow blow fuse mirrored the shop's opinion.
I was going to the local shop I was telling you about to purchase the MG Chemicals contact cleaner tomorrow and they had fuses (thought I should stock up and also to check what the Jolida manual states) and after reading the manual I found out they put fast blow fuses in the thing.
That's when I became a bit confused!
Paul
Follow Ups:
fast blow fuses are just normal fuses. Not to be confused with slow blo fuses.
If the fuse is blowing at turn on, did the upgrade include larger value power supply capacitors vs. the original capacitors?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
This is what was done to it when we modded it - these are Jim's words I am copying and pasting here...
1. replace the R17 & 18 1 Ohm 5 watt(!) resistors with
1 Ohm 1 or 2 watt.
2. Remove the 220uf/300 volt C6 & C7, replace with 680uf/250 volt
Panasonic ED. Save the 220/300, we'll reuse them.
3. Add (3) missing bypass caps, use .68uf GE MPP caps
(if the board doesn't have holes for them don't do it).
4. Replace C8 & C9 470/400 with 220/300 just removed
4a. (Option) Add .15 mh choke from in series with each B+
feed to the output transformers. If you don't add these chokes
leave the 470/400 caps in place
5. Replace stock diodes with UF5408 fast Vishay diodes
6. Replace the bias diode VD5 with a GI 856 fast/soft diode.
7. Replace R13 & R16 with 10K (or 1K if originally equipped)
carbon composition resistors
8. Replace the coupling caps - use .47uf/600 volt Rel-Cap
PPFX for C1 and .22uf/400volt K40 PIO (body insulated
from PC board) for C3 and C4.
Paul
4. Replace C8 & C9 470/400 with 220/300 just removed
That would lower the turn on surge current, not increase it.
Does the fuse blow at turn on?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's done it at turn on and also within anhour. All new tubes in the thing too. They tested fine.
Paul
There has to be a leaky cap somewhere.
I would look at the caps that used to be C6-C7 that are now in the C8-C9 position.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I sent the parts to Paul in January of 2009 - so the now 8 year old caps that were installed then should be fine. But the relocated 220 uf caps are getting a bit long in the tooth so I agree with Tre. They could be acting up.
It might be wise to replace them just as a matter of course after all the years of service.
Paul
If you did all that,that would be a McShane and I'm sure it made a hell of an improvement.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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