Tube Tech MP1A weirdness

[Nele]

here's the psu schematic. +48V is phantom and 33V is heater. the 2200uf cap is 1000uf in my unit.

 

[gyraf]

..early units used the 48V for heater - just added a series resistor...

Jakob E.

 

[Nele]

aha.. this is a newer one with 33V for the heaters.
I've replaced the heater psu-cap and things haven't improved

 

[pucho812]

aha.. this is a newer one with 33V for the heaters.
I've replaced the heater psu-cap and things haven't improved

replacing caps willy nilly without valid reason would be  a waste of cash... 

 

[Nele]

If there is ripple then there  could be a bad electrolytic cap or several bad electrolytic caps in the PSU

well, I replaced the cap because there was ripple on the 33V/48V psu, just as you suggested...? we're talking $ 0,25 here so always worth a try . or is there a way to check which capacitor in the psu might be faulty?
I just realized that because all the tubes have their heaters in series with each other, removing tube 1 means the other tubes won't get heater voltage making measurements etc impossible.

cheers,
corneel

 

[pucho812]

correct I did say that. and yes no harm no foul.


checking for caps, use a multimeter and make sure you de-solder one side of the cap to see if it is working much like checking resistors.


which side had the ripple? 33V or 48V?  did you go over the solder joints?

 

[Nele]

checking for caps, use a multimeter and make sure you de-solder one side of the cap to see if it is working much like checking resistors.

I've always found testing caps with a multimeter a bit unreliable because the testconditions are not the same as the in circuit-operation. I recently replaced a fairly new multi-cap in a Leslie 147 for instance which measured ok but turned out to be fried.

which side had the ripple? 33V or 48V?  did you go over the solder joints?

both..

 

[pucho812]

did you go over the solder joints?

 

[Nele]

Here's a version of the schematic with differences from Jakob's original in red. On the bad channel the zobel-capacitor of 47nF measures 72nF.. Could this be a cause of the problem?

 

[Nele]

did you go over the solder joints?

yes, but as I had to disassemble the unit to do so I haven't been able to check if it had any effect yet. stay tuned

 

[pucho812]

cool o.k. keep us posted

 

[Nele]

Pucho, hot damn, I owe you one. looks like re-soldering all connections fixed the damn thing..
Let me know when you're in The Netherlands and I'll buy you a beer!

I'll do some more testing tomorrow just to be sure.

Thanks everyone!

 

[pucho812]

your welcome.. I'll take you up on that beer but I doubt I will be in Europe anytime soon... 

 

[okgb]

More like a MP-1A thread ?

I have a friends here and he is getting a crackling
when the phantom is engaged , with no mic connected
I'm reading 82v dc , which doesn't make me want to attach
a mic to hear it , I Lifted one of the phantom resisters and
it is 6.8k , so other than resoldering , which i will do
Anyone else heard this problem  [ and solve it ? ] before ?

a handful of parts in the psu , i guess
[ which i can see where the traces of the bigger watt resisters
have burned off and been replaced with parts leads ]