Vox AC30HW2 Vietnamese Hand-Wired Combo

[Bluto]

Hey All,

I have scoured the interwebs and have found very little information regarding The Vietnamese Hand Wired AC30. I took one on trade for some guitar work a while back and my immediate impressions were that it sounded good yet not as rich in content and feel as other AC30 or AC30 type amps that I've had (Hayseed 30, Matchless DC30, Matchless Lightning, Vox AC30/4, Vox AC30TBX, Orange AD30, Bad Cat Hot Cat 30 and a few more experimental amps that I've made)

First I removed anything that had been added to the power section and top boost channel that didn't reflect the original 1964 Vox Schematic. Secondly I replaced all on-board components with good quality... (CTS pots, mallory carbon comps, F&T filters @ 1964 values, Sozo signal caps) The Ceramic resistors & thermistors were of good quality and spec'd as they should be.

Speakers are 1) Celestion Blue 15ohm and 1) Celestion Gold 15ohm (added the Gold for a slight bump in headroom)

Tubes=Sovtek 5AR4, Matched Quad early 60's RCA EL84, RCA Long Plate in the PI, Amperex Bugle Boys in Positions 1 & 2.

Still, it sounds Great but seems to be missing that certain something that makes you go Ahhh and falls a tad short of that "Kranggg" and shearing steel effect that we all seek out in our AC30 type amps (at least I think that's what we're all looking for).

Therefore one could conclude that there may be a shortfall in the stock transformers yet I have failed to find out anything about them... where they are made? by whom? and to what spec? Are they supposed to favor Haddon? Woden? Drake? I don't hear any specific artifact that would lead me to compare them to any of these.

Does anyone have any experience / information regarding this amp? Specifically the transformers. What are some choices that you have made in transformer swapping and what were the results?

Thanks in advance,

Bluto

[Colossal]

Sorry, I have no idea what's in your amp, so I can't help you there, but the transformers are very important. Some things to consider...

1) Get the B+ voltages right. The original Haddon power transformer was 285VAC secondary, unloaded (117VAC mains). Loaded and rectified with a good GZ34/5AR4, the B+ will be 315-320VDC.
2) Get the right choke. The original was a Radiospares 20H 460R 100mA.
3) Get either a Haddon or Woden style output transformer. The later Albions had a different sound, although some really like that generation.

[Bluto]

Thanks Colossal,

Yes depending on the brand of rectifier i get between 312V & 316V. The Sovtek came in a bit lower than JJ, Sylvania, Mazda or GE. Honestly I havent acually checked the ?-0-? on the PT yet but I do know that there's only about 3/4 the iron in the stock PT as there is in Heyboer and Mercury's that i've used. Very suspicious.

Same goes for the Choke , the stock is tiny and by the looks of it can't be more than 10H.

I have a set of Heyboers that I was going to use for a scratch build and I'm tempted to put them in this amp. I Know I Love the sound of the Heyboer. My Hayseed 30 was just incredible with them.

[Colossal]

Thanks Colossal,

Yes depending on the brand of rectifier i get between 312V & 316V. The Sovtek came in a bit lower than JJ, Sylvania, Mazda or GE. Honestly I havent acually checked the ?-0-? on the PT yet but I do know that there's only about 3/4 the iron in the stock PT as there is in Heyboer and Mercury's that i've used. Very suspicious.

Same goes for the Choke, the stock is tiny and by the looks of it can't be more than 10H.

I have a set of Heyboers that I was going to use for a scratch build and I'm tempted to put them in this amp. I Know I Love the sound of the Heyboer. My Hayseed 30 was just incredible with them.

Well, your voltages are spot on, so that's great. You might swap in that Heyboer OT. For sure, that is going to be an improvement. Have you measured the DC resistance of the stock choke?