Harmony

[RectifiedAmps]

Replacing leaky capacitors in the signal path can definitely change the sound in unpleasant ways. The old leaky ones would likely ‘brown’ out the sound a bit, as the DC they let pass would cause the downstream gain stages to bias hotter (towards grid-limited clipping), and maybe reduce gain a bit.

Drifted resistors are an easy one to suss out because you can simply measure them once removed to see how far they’ve gone.

I imagine the speaker is hardwired straight to the output transformer, but you could desolder it and rig up a temporary jack to try a different speaker. Really old ceramics don’t often hold up well with time (but YMMV).

[RectifiedAmps]

This may be of interest too:
https://oldamps.weebly.com/harmony-h307x.html

[Slowy]

Replacing leaky capacitors in the signal path can definitely change the sound in unpleasant ways. The old leaky ones would likely ‘brown’ out the sound a bit, as the DC they let pass would cause the downstream gain stages to bias hotter (towards grid-limited clipping), and maybe reduce gain a bit.

Drifted resistors are an easy one to suss out because you can simply measure them once removed to see how far they’ve gone.

I imagine the speaker is hardwired straight to the output transformer, but you could desolder it and rig up a temporary jack to try a different speaker. Really old ceramics don’t often hold up well with time (but YMMV).

Clarry commented the the bias was way off; like twice what it should be. And I was just thinking about a lug to jack socket lead to try different speakers.

[Slowy]

This may be of interest too:
https://oldamps.weebly.com/harmony-h307x.html

Cool, thanks! That's my baby...

[Slowy]

Haven't been able to sort a cable for speaker swapping yet but I replaced the 12AX7 with a 5751. It improved things considerably. I'm reasonably sure the remaining harshness is the speaker breaking up.

But regardless, the harshness can be controlled just by turning it down a bit.

[k1w1]

Good to hear the sound is coming back, those speakers Harmony used were not always the best, my H400A I swapped out the stock for a 60s Jensen and the Valco made 8148 I found a 60s speaker to fit that had the same output tranny on the speaker basket. That is the one Ryan recapped for me and did a great ob.

I asked over at the Harmony forum but no one had any info but did provide a blow up of the schematic Rectified Amps linked, it may be of use

harmony-h307x-2_orig by Laurie Franks, on Flickr

[Slowy]

Just took the Harmony back to its previous owner for an assessment. He pluggd in a LPJ with single humbucker (You're not the only one, Grant) and proceeded to make it sound wonderful.
I took note of his settings which were different to what I'd been doing, but I got what I was looking for; the amp's just fine. Stop fussing and learn to play it!