The guts of the AC30 HW amplifier

[paologregorio]

I bought a "scratch and dent" AC30 HW a few months back at a steal of a price. The cabinet needed some slight repair, requiring the removal of the amp chassis, so I was able to take some pics of the amp's internals. Since they differ from the standard AC 30, I thought I would share the details here on the forum.

Back panel photo showing placement of preamp tubes unique to this model AC30; the preamp tubes on most AC30 models are mounted horizontally on the opposite side of the chassis pointing out towards the front of the amp.

Front side of panel chassis showing stripped down look afforded by lack of preamp tubes facing forward

The HW circuitry is a bit more spare than most other AC30s as there is no vibrato, and only two, rather than 3 channels

Top side control panel showing the simple, two channel layout with triode/pentod switch, and overhead view of transformers and power tubes. Apologies for the poor photo quality

Those of a serious technical mind wrt amps feel free to compare/contrast this amp, as well as correct any errors I may have stated wrt this amp, which is a real screamer. I really appreciate the pentode/triod mode available for both channels of the amp.

[paologregorio]

For comparison, here is the tube layout on a Korg AC30 TBX, as photographed by North Coast Music:

As you can see, on the TBX models, (as well as the CC models), the tubes are all on the front side of the chassis

Interestingly, unlike the original AC30s, as well as the CC and HW series, the power and rectifier tubes are mounted horizontally on the Korg TBX models, rather than vertically as with the original, CC, and HW series amps.

[8mileshigher]

Very cool ... now lets see some photo's of the insides of your other AC 30s for comparison !
Regards

[collin]

Circuit board, eh?

I always thought the HW series were point-to-point. ah, well....

[paologregorio]

It's not exactly circuit board; it's more like the modern equivalent of eyelet board for idiots; the board appears to have a silhouette and label for the proper location of where each component is supposed to be soldered.

[soundmasterg]

They also use turrets on the board instead of wave soldering, which greatly increases reliability and ability to withstand rough treatment.

It is the same way Randall Aiken makes the boards in his amps and is one of the best ways to make a board IMHO.

Greg

[wmthor]

Paul, thanks for sharing.

[paologregorio]

They also use turrets on the board instead of wave soldering, which greatly increases reliability and ability to withstand rough treatment.

It is the same way Randall Aiken makes the boards in his amps and is one of the best ways to make a board IMHO.

Greg

Ah, interesting, I did not know that. Thanks for posting.

I also should have said that the screening on the board "idiot-proofs it" wrt part placement, and the silhouettes and parts labels facilitate speed and ease of assembly/wiring. It was late, I was tired.

[paologregorio]

I usually use a different AC30 for rehearsal, but I used this one instead last night, opting for the EF86 channel, with the briliance switch on "1", pentode mode, and the bass shift switch in the "1" position; the amp sounds fantastic! It has lots of bottom end while still retaining the mids and highs. I had the amp volume only up at around the equivalent of 2 or 3, but it had the tone my other AC30 usually has to be louder for. Pentode mode is great at lower volumes and really gives the amp more oomph and presence. The EF 86 channel is quite special.

[soundmasterg]

I usually use a different AC30 for rehearsal, but I used this one instead last night, opting for the EF86 channel, with the briliance switch on "1", pentode mode, and the bass shift switch in the "1" position; the amp sounds fantastic! It has lots of bottom end while still retaining the mids and highs. I had the amp volume only up at around the equivalent of 2 or 3, but it had the tone my other AC30 usually has to be louder for. Pentode mode is great at lower volumes and really gives the amp more oomph and presence. The EF 86 channel is quite special.

Now you know why everyone goes so nuts over EF86's! They sound great at high volumes too....you should try it sometime.

Greg