Harmony H-420 (schematic confusion)

[rafe]

Schematic depression searching my soul......Picked up a 420 off of e-bay  I have the chassis on the bench, and it looks like I'm the first in there and it looks good. I am planning on the electrolytic caps filter and bypass(6caps) to be replaced' a 3-prong installed, the 2 .01 ac caps removed. is the neon lite safe where it is?  ...I am working off the schematic where C supplies the plates on V2 PI then mysteriously turns into D (as it is clearer.) This amp is very much like the thunderbolt I have .....but it's been a long time since I was in there, It had the double (reversing polarity) but I don't remember 2 ac caps. I am going to test the amp as-is everything looks good and i am considering leaving the smaller caps as-is. Thanks for any insights you may offer, Rafe   Harmony_h420.pdf

[bmccowan]

Congrats on picking up a sleeper. The good news is you can buy them cheap. The bad news is that you need to sell them cheap. As you state - it's the SS rectified Thunderbolt in a different chassis and cabinet. I've rewired two of them and one Tbolt. There is also a Tbolt with a tube rectifier. Interestingly there are inaccurate Tbolt schematics out there, but the H420 schematic I used was spot on.
I left the AC lamp as it was - but I did not spend time thinking about that. I believe it's safe.

schematic where C supplies the plates on V2 PI then mysteriously turns into D

I think that the "D" should really be at the junction of those 2 100K resistors. I think you will find that the cap at that node is not a 4uf but is a 0.1 or a 0.01. The 4uf ? seems to trace back to one schematic. I kept the values of the filter caps the same, but used a 33uf in place of the parallel 20/10 caps. I re-wired the power switch as a single pole. Good discussion here: https://el34world.com/Forum/index.php?topic=26084.0
 

[rafe]

I see a .1 there. I brought it up slow on the variac ....it came with a 20amp fuse, calls for a 3amp slow-blo I am out of them but have some 2 amp and that worked. checked voltages as I brought it up. no tubes at first all voltages were reasonable for no tubes. Put in a set of tubes I scavenged out of stash because the tubes in it were 1965 rca's 2 12ax7a's and 2 6l6gc I don't think they have much time on them and didn't want to risk them ....Voltages look very close to the specs with the tubes in none of the caps showed any leakage I ran it for an hour and checked again voltages good. Then I played it for an hour or so, really nice my shop speaker is a 2x12 closed cab.
Still need to do the 3 way Those .01 caps are coming off the fuse, I am wondering if they can stay? My thunderbolt is rectified I have the filter caps here and I will keep thinking about installing them as I clean the cabinet and grillcloth and play the amp. Nothing has been touched in the amp 61 years old and going strong, Outstanding!

[rafe]

"I kept the values of the filter caps the same, but used a 33uf in place of the parallel 20/10 caps."


That was my thought too. Makes you wonder why they did that, probably had lots of 20's and 10's on hand.
My Dad bought me an H420 when I was 12 I was playing bass and it served me well for 3 years until I worked  all summer and bought a brand new 68 drip edge bassman ....."Well, It took me years to get those souvenirs' And I don't know how they slipped away from me"