HH Scott Restoration and Cabinets/Installing unit.

Measure the one that's not broken and see if you get a solid ohm reading or not. In-circuit is fine.
 
Vintage -- The components you refer to are capacitors, and of very small value -- typically less than 1 pF. On the 299C-C1 schematics I have, these would be identified as components C9 and C109, with a value of 0.68 pF each.

Their purpose is to counteract cross-talk that would otherwise occur at very high frequencies between the channels due to the small capacitance values that exist between the various switch terminals, between the channels, on the Mode switch. If you remove them, you will almost certainly not be able to hear any difference, with the benefit they offer really only being demonstrable on an O-scope. To replace it, you will need to go to one of the large part houses like Mouser or Digikey to find a replacement. The voltage rating of the component is quite uncritical, as there is no DC voltage impressed across these caps. Therefore, even the lowest voltage rated piece will work.

I hope this helps!

Dave
 
Vintage -- The components you refer to are capacitors, and of very small value -- typically less than 1 pF. On the 299C-C1 schematics I have, these would be identified as components C9 and C109, with a value of 0.68 pF each.

Their purpose is to counteract cross-talk that would otherwise occur at very high frequencies between the channels due to the small capacitance values that exist between the various switch terminals, between the channels, on the Mode switch. If you remove them, you will almost certainly not be able to hear any difference, with the benefit they offer really only being demonstrable on an O-scope. To replace it, you will need to go to one of the large part houses like Mouser or Digikey to find a replacement. The voltage rating of the component is quite uncritical, as there is no DC voltage impressed across these caps. Therefore, even the lowest voltage rated piece will work.

I hope this helps!

Dave

Thanks Dave, That was a huge help! I have the same schematic but really wasn’t sure what I was looking for. Thank you again for responding and being so willing to help.
Dave C
 
Let me say how any of us can make a dumb mistake that will make a body go crazy..
I kick myself every restoration job, cause I ALWAYS seem to make a bone head mistake. Fortunately, tube amps are troopers and I haven't destroyed anything yet. But I kind of think it's that extreme stress, despair and frustration...followed by the glorious relief and satisfaction (when you discover and correct the problem ) that make this hobby so addicting.

Kind of reminds me of the Dennis Leary quote.." Smokers are the only people who know what it's like to want something REALLY F***KING BAD and get it, over and over and over again"


I was measuring voltages on my LK-72 this weekend and measured 724 VAC on my PT secondary. DC voltage after the GZ34 was 426. Does that make sense? OP said his Heyboer was 370V secondary. These are supposedly the same amp I thought.

Voltage after the first 33ohm 10W resistor in the filter was 419 (should be 455 per the schem....8% low).
 
I don't have the schematic close at hand, but can't you determine what they are from looking at the schematic?
 
Schematic doesn't say what the secondary should be.

It DOES have rectified voltage values (455V).
 
I kick myself every restoration job, cause I ALWAYS seem to make a bone head mistake. Fortunately, tube amps are troopers and I haven't destroyed anything yet. But I kind of think it's that extreme stress, despair and frustration...followed by the glorious relief and satisfaction (when you discover and correct the problem ) that make this hobby so addicting.

Kind of reminds me of the Dennis Leary quote.." Smokers are the only people who know what it's like to want something REALLY F***KING BAD and get it, over and over and over again"


I was measuring voltages on my LK-72 this weekend and measured 724 VAC on my PT secondary. DC voltage after the GZ34 was 426. Does that make sense? OP said his Heyboer was 370V secondary. These are supposedly the same amp I thought.

Voltage after the first 33ohm 10W resistor in the filter was 419 (should be 455 per the schem....8% low).
If you are measuring between pins 8 and 2 of the rectifier socket that is not unusual
 
724 plate to plate is a 362 volts plate to ground at the rectifier. 362 vac through a full wave is 506 volts, DC less about 20 volts for loss through the rectifier and it should be about 485 vdc to ground straight off the rectifier, assuming it has a cap to ground right off the rectifier. If there is a resistor between the rectifier and the first cap the voltage will drop. If its too low I'd wonder if that rectifier is healthy.

Honestly 8% isn't anything to worry over. Most of those voltages were given with at least a 10% margin, and being a smidge low is probably better than being high which a lot of HH Scott stuff seems to have trouble with. If its really a concern you can always make the resistor smaller to bump the voltage.
 
Vintage -- The components you refer to are capacitors, and of very small value -- typically less than 1 pF. On the 299C-C1 schematics I have, these would be identified as components C9 and C109, with a value of 0.68 pF each.

Their purpose is to counteract cross-talk that would otherwise occur at very high frequencies between the channels due to the small capacitance values that exist between the various switch terminals, between the channels, on the Mode switch. If you remove them, you will almost certainly not be able to hear any difference, with the benefit they offer really only being demonstrable on an O-scope. To replace it, you will need to go to one of the large part houses like Mouser or Digikey to find a replacement. The voltage rating of the component is quite uncritical, as there is no DC voltage impressed across these caps. Therefore, even the lowest voltage rated piece will work.

I hope this helps!

Dave
AHA! I've been staring a hole through C9 and C109 on my 299C and LK-72 schematics, hoping in vain for some enlightenment to strike me, wondering why on earth there are 0.47µF (on the LK-72) or 0.68µF (on the 299C) caps connecting the two channels, and where the heck they are on the chassis. Well, so you're telling me they're 0.47 PICOFarad caps, and they're for high-frequency crosstalk prevention?
Thank you for solving this perplexing mystery for me.
 
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