Hum in right channel, developed a few months in

[eudisld15]

You've made things worse by replacing more than what was recommended.  The MJE350 and PN2907 on the center low current board were working properly and giving the correct voltages, now they are not. 

This is about the point where sending the kit in for repair starts to make a lot more sense than continuing here.

Very interesting development. I didn't see this message until now. So I also replaced the LM431 on the B side on the low power board but not the other two. Now Voltages look better and when listening with the tubes in it sounds much better. No buzzing but the overall volume seems lower. There isnt and significant balance issue on each side

But there are still some discrepancies.

With the 6AQ5s on the Low current board the OA and OB are low as well the IA and OB on the high current C4Ss are out of range.


With 6AQ5s
Low Current C4S

IA 149
OA 45.6
KregA 5.93
bRegA 148.9

IB 149.5
OB 46
KRegB 5.9
bRegB 149.5

High Current C4S (closest to power inlet)

IA 199
OA 149.5
bA 0
IB 0
OB 79.7
bB 149.5

High Current (furthest from power inlet)


IA 199
OA 148.9
bA 0
IB 0
OB 75.8
bB 148.9

[eudisld15]

Also forgot

No 6AQ5s

Low Current C4S

IA 209
OA 39
KregA 0
bRegA 209

IB 209
OB 40
KRegB 0
bRegB 209

High Current C4S (closest to power inlet)

IA 211
OA 209
bA 0
IB 0
OB 98
bB 209

High Current (furthest from power inlet)

IA 211
OA 209
bA 0
IB 0
OB 100
bB 209

[Paul Birkeland]

You still have an issue on the center board now, but your regulators are working.  Can you post a photo of what your center board looks like? If you put the PN2907 transistors in backwards, that would make the issues you're having.

[eudisld15]

You still have an issue on the center board now, but your regulators are working.  Can you post a photo of what your center board looks like? If you put the PN2907 transistors in backwards, that would make the issues you're having.

Sorry for the delay. Had some stuff come up.

Hmmn I put the flat side towards the center.

I used PN2907A transistors as listed in the manual.

See the attached image.

[Paul Birkeland]

Well, whatever happened, it happened to both channels.  Do you have the old transistors still?  If you put them in, the amp may work properly.  Otherwise I would be looking for soldering problems on the bottom side of the board or issues with the 9 pin socket wiring.

[eudisld15]

Hey, sorry for the delay. Life has me busy.

So I noticed the center LEDs on the 9 pin socket looking a bit melted. Replaced both and BAM! everything is measuring within 10% again! The amp sounds great once more. I love it.

Here's some pictures of the final build for you all to enjoy.

[Paul Birkeland]

That's an interesting finish on the plate, what is it???

[eudisld15]

Ah it's a plaint finish

The aluminum plate was primed with high build urethane primer. Then a basecoat of urethane glossy black, 2 layers. Then I sprayed house of kolor marbalizer. I made it an extra thick and wet layer and then used plastic wrap to dab it while it's wet. This gives it the marble effect. Finished it in 1k clear (a huge mistake, if I end up getting a sex or mainline I'll do it in 2k clear)

[Doc B.]

Looks very cool. And yeah, we all make the 1K vs 2K mistake. Rattle can 2K clearcoat rules. Totally worth the money, particularly if you line up enough projects to use up the can before it kicks. We use it on our race bikes.

[eudisld15]

Looks very cool. And yeah, we all make the 1K vs 2K mistake. Rattle can 2K clearcoat rules. Totally worth the money, particularly if you line up enough projects to use up the can before it kicks. We use it on our race bikes.

I have a detailer hplv air brushsetup for such projects but at that time I had some 1k I wanted to try went with it. Takes for ever to fully harden. Never again. I normally always use 2k for projects like image attached and I'm definitely sticking to it. Haha. I'm still a newbie when it comes down to hobby painting and stuff. I bet you guys do some cool stuff with bikes.

[Karl5150]

You guys lost me at 1K vs 2K, but that finish looks pretty sweet, as do the other pics.
Karl