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Questions on Harmony H410


 
8/2/2005 3:18 PM
Carlo Pipitone
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Questions on Harmony H410
Hello fellow Ampagers,  
 
I have bought a stock '65 Harmony H410 amp.  
It's a sweet crunchy little baby that only needs some minor overhaul (cap job and a few drifted resistors).  
 
I have two questions:  
 
1) wouldn't it be wise to put a fuse somewhere? If so, where?  
 
2) the schematic shows a .1uF and a 1uF caps in the tremolo circuit (which is driven by a 6AU6 tube). In the amp there are two .47 caps in those places (red spots in the schematic, see the link below). Those are two nice, huge, sturdy red caps (don't know their brand). Do you think I should put the original values in both cases? Or may I leave them alone?  
 
The schematic is here:  
http://www.accordo.it/upload/1123017160/harmony_h410_partial.jpg  
 
TIA,  
Carlo
 
8/3/2005 2:06 AM
Chuck
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Those caps in the trem only serve to make the tube oscillate and alter the voltage on whatever part of the circuit is tremoloed (is that a word?). So they aren't in the signal path. If the trem is working to your satisfaction you can leave those caps alone. There is no tone improvement to be had by changing them.  
 
Chuck
 
 
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8/3/2005 3:18 AM
Carlo Pipitone
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I see...  
 
Aren't the bias modulating caps the C5-C6-C7 .02uF caps?  
 
Carlo
 
8/3/2005 9:25 AM
Chuck
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Well I'm no expert on trems. And I hadn't looked at the schem before. C5, C6 and C7 are part of a phase reversal circuit used to make the 6AU6 oscillate. C10 (in red) looks to be for shaping the envelope and C11 (in red), well, I'm not sure. But none of them are in the signal path. They only effect the the oscillator tubes oscillation. So If it's oscillating, and you like the effect and envelope, then it's good.  
 
Chuck
 
8/3/2005 1:06 PM
Carlo Pipitone
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Thanks Chuck.  
 
If the circuit works like in BF/SF Fenders, those C5, C6 and C7 (tied to the tube's plate, pin 5) should be involved with the oscillation speed.  
Do you agree?  
 
I ask because I do want to decrease the speed rate subbing a larger cap in there.  
 
Carlo
 
8/3/2005 8:29 PM
Chuck
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I'm really going out on a limb getting involved in a trem related post...I've never built or owned an amp with a trem. But IIRC the Weber book suggests increasing the value of the last cap in the phase reversal circuit to slow down the trem.
 
8/5/2005 3:11 AM
Carlo Pipitone
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Ok, thanks! (nt)
no text
 
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