How does this schematic look to you? (Harmony 430, Valco)

[Duncan]

So I have an old Harmony 430 amp that I absolutely love, however, it's super difficult to work on, and I want to make improvements to the layout. And since I only ever use one channel, I figured I would have a go at recreating the schematic, but with just one channel (no tremolo or reverb).

I think I've got it right, but I'd love to hear your input. I plan on building this into a gutted Hammond A0-43 chassis and using its transformers.

Thank you in advance!

[Latole]

Schematic

[tubenit]

Years ago, I had a DanElectro 275 Centurian amp. I truly regret selling it.  I had this idea that I could rebuild it "new" into a tweed style chassis. So, I followed the schematic carefully and built a new one as a one channel into a beautiful cabinet. I used new Hammond PT and OT.


When done .......... I had a nice sounding amp but it sure didn't sound like the Dano I loved so much.  This is the only amp I regret ever selling. I hope your results prove much better than my did.


With respect, Tubenit

[SEL49]

I made 3 corrections to your schematic.

[passaloutre]

Years ago, I had a DanElectro 275 Centurian amp. I truly regret selling it.  I had this idea that I could rebuild it "new" into a tweed style chassis. So, I followed the schematic carefully and built a new one as a one channel into a beautiful cabinet. I used new Hammond PT and OT.


When done .......... I had a nice sounding amp but it sure didn't sound like the Dano I loved so much.  This is the only amp I regret ever selling. I hope your results prove much better than my did.


With respect, Tubenit

Just curious, what’s your guess on why the clone didn’t match the original? Transformers?

[tubenit]

Just curious, what’s your guess on why the clone didn’t match the original? Transformers?

I don't know for sure?  I think the Hammond OT probably had alot to do with it. I say that because at one point I put a Deluxe Reverb OT in the original Dano Centurian.  It lasted about 30 minutes in there & I put the original back in. The DR OT lacked the warmth and "grind" of the Dano OT.  For lack of a better description, the DR OT sounded sorta sterile and brittle to me.


I'm also thinking the Dano cabinet (which was lousy quality) impacted the tone.


Again, my attempt left me a nice amp but it wasn't close to the great warmth and on the edge of "overdrive" that the Dano amp had.


with respect, Tubenit

[Merlin]

In your schem V2a is missing its anode resistor.
Interesting input jack configuration, and surpringly low supply voltages to V1! And a mute (standby) switch too, quite unusual.

[Duncan]

I made 3 corrections to your schematic.

Yeah, I made some corrections and updates to my schematic based on feedback here and over on TGP.

New one attached.

[bmccowan]

So I have an old Harmony 430 amp that I absolutely love, however, it's super difficult to work on

I feel that pain. I have a National and Gretsch branded versions of that amp. The way Valco hid signal caps on the back side of terminal strips makes for a slow and messy task. I finally resorted to photos and sketches of the lead connections. Cut the leads at tubes/pots, etc. and remove the terminal strip. Once out of the amp, the caps and resistors are easy to replace. Seems like a lot of effort, but its better than the finger contortions otherwise needed. Does anyone make a gooseneck soldering iron?
Should be a great project. Finding the right OT will be key, I think.
Sluckey has a nice layout for a similar Valco on his site.

[Duncan]

So I have an old Harmony 430 amp that I absolutely love, however, it's super difficult to work on

I feel that pain. I have a National and Gretsch branded versions of that amp. The way Valco hid signal caps on the back side of terminal strips makes for a slow and messy task. I finally resorted to photos and sketches of the lead connections. Cut the leads at tubes/pots, etc. and remove the terminal strip. Once out of the amp, the caps and resistors are easy to replace. Seems like a lot of effort, but its better than the finger contortions otherwise needed. Does anyone make a gooseneck soldering iron?
Should be a great project. Finding the right OT will be key, I think.
Sluckey has a nice layout for a similar Valco on his site.

Haha funny story, a little while back, I posted a “How would you lay this tone circuit out on a turret board” thread, and Sluckey posted how he did it. Incredibly helpful.

The OT is going to be the one from the Hammond husk I’m building this in (A0-43). Hoping it scratches the itch.

[bmccowan]

The OT is going to be the one from the Hammond husk I’m building this in (A0-43). Hoping it scratches the itch

I bet it works fine - I've used similar OTs from AO-39s for EL84, 6973, and 6V6 amps to good effect. Of course, this might just prove that my hearing is not very discerning.

[Lectroid]

I've used the OT twice in 6V6 p-p amps.  Works great.  I used the A0-43 PT to make a good DR 1-channel amp with 400V to the power tubes.