Harmony H415 weak tremolo

[punkykatt]

Hey guys, any way to strengthen the tremolo on this amp? I have to turn the intensity  up to 75% before you can hear it. It uses the 6AU6 pentode. All the resistors and caps read close to spec, and the voltages are close to whats on the schematic.  Any suggestions are much appreciated.  Thanks in advance. Punky

[Willabe]

Here's a clearer/cleaner schemo.

http://el34world.com/charts/Schematics/files/harmony/harmony_415.pdf


                 Brad     

[punkykatt]

Thanks Brad for that clean schematic.

[terminalgs]

assuming its not functioning as the engineer intended:

Did you check out C19 .1uf to make sure it is A-OK ?


otherwise:


R29 and R28 form a voltage divider network for the oscillating AC sine wave,  no doubt a bigger version of that signal exists closer to the plate, or at the plate.

[sluckey]

...any way to strengthen the tremolo on this amp?

First off, have you tried a new tube?

Following terminalgs thoughts...

Did you check out C19 .1uf to make sure it is A-OK ?

Decreasing the size of that cap to say .047µF will slightly increase the strength.

R29 and R28 form a voltage divider network for the oscillating AC sine wave,  no doubt a bigger version of that signal exists closer to the plate

Connecting C18 directly to the plate should give a pretty big increase in the LFO signal.

[John]

FWIW, there's plenty of tremolo in the stock circuit if everything's working right. Just echoing the other guys, I'd try swapping the tube first.

[punkykatt]

Thanks for the replies everyone.   Tried another 6AU6 tube (no change). C19 reads 0.104uf on my cap meter. Connected C18 directly to the plate and (hot dang)  get nice strong tremolo.  Thanks again guys.     Punky

[Willabe]

Connected C18 directly to the plate and (hot dang)  get nice strong tremolo. 

               

[terminalgs]

Thanks for the replies everyone.   Tried another 6AU6 tube (no change). C19 reads 0.104uf on my cap meter. Connected C18 directly to the plate and (hot dang)  get nice strong tremolo.  Thanks again guys.     Punky

If you're still in a tinkering mood, lift either leg of C19,  see if trem level changes.  If its the same, replace C19, and move C18 back to original locale. see what happens.


cap meter sez .1uf doesn't mean its working correctly in that circuit. afterall, it is 50yrs old.


If you are done tinkering,  rock on.  'clap for the wolfman' is fav tremolo song of mine, was listening to it just this evening.

[Willabe]

'clap for the wolfman' is fav tremolo song of mine

Yeah, love it.


                   Brad     

[punkykatt]

Thanks terminalgs,  I got`er buttened back up and a big smile on my face for now.  For a bargain bin amp this thing really  screams and takes pedals well after doing some miner mods to the preamp. 

[John]

Punky, do you mind sharing what mods you did? When I refurbished mine I kept everything stock and love it. I have often thought about tacking in a cathode cap on the preamp tube just to see, but never have gotten around to it. Thanks!

[punkykatt]

John,  channel 1, I tacked in a 2.2uf cathode bypass cap on the existing 1.5k.  Channel 2, I got rid of the grid leak bias setup and went with the
Fender type setup 1M grid to ground, 1.5k/4.7uf  on the cathode.
Punky

[John]

Cool, thank you!