And now for something completely different!

[galaxiex]

The StewMac tools do not appear to hold the shaft in place. That is what you need. The shaft does not move, only the knob.

Well your point was not very clear...

You also said this...

The StewMac tools do not appear to hold the shaft in place. That is what you need. The shaft does not move, only the knob.

Which seemed to imply you thought there was a way to hold the shaft.

[Boy Howdy]

Well, sorry to disappoint but gave up on the knobs. I had been trying to change one resistor on the ch. 2 board from the back side and was having a difficult time with it. That's the only reason I was considering removing it. But I was finally able to get that resistor replaced, so no need to remove the board.

The resistor I removed is one of two 470Ks that effect the tremolo speed. One of them was reading 390K so I thought that since I wanted to slow the trem anyway, I'd replace it. I put in a 1 meg which took it from 160BPM to 140BPM. Still not quite where I want it. I'll probably go to a 1.5meg. I don't normally like tremolo, but this one is really nice. I'm after that slow and sexy Fender Rhodes trem sound.

BUT I HAVE ANOTHER QUESTION:

When I got the amp it had a bad R311 resistor on the power amp board. It functioned but sounded bad. It was visibly burnt, so I replaced it with the same value (560 ohm / 5 watt). It fixed the problem. But it seems hotter than it should be. And smells mildly of roasting electronics. It's also starting to turn brown. This resistor drops the voltage from 75 to 40. I measured ~70 to ~35. Should I change this resistor to a 10 watt?

[TomCarlos]

Corrected - R311 is not 560K !!! It is 560 ohms.

Here is the schematic for the Power Amp module.

[Boy Howdy]

Hey Tom, where you getting 960 from? Looks like 560 to me. I checked another schematic as well. '560K' was a mental typo. I meant 560 ohm.

[TomCarlos]

Dang.... I need my glasses. Sorry... 560 ohms is correct. I will correct that post....

With 75 volts on one side and 40 on the other, that leaves 35 volts across the resistor.

Power Dissipated = (35*35)/560 = 2.18 watts

[oc disorder]

Well as far as a knob puller is concerned for future reference may I recommend an Aussie barbecue fork. You may have to put some cloth or felt under it to prevent front panel scratches and I would recommend rotating the knob and lifting at different points.. Please see attached technical photos. Regarding the 5watt resistor I would think that something in the front of the amp that runs from 40v is drawing too much current ! ,As it is still dropping the required 35v perhaps there is not a problem so a larger wattage resistor should stop some of the heating effect that is discolouring the board ! Of course it then looses it's ability to act as a fuse !!

[Boy Howdy]

You scared me, Tom. And it ain't even Halloween. Those handwritten numbers are a pain on those ACC schems. You can't tell the difference between the 3s and the 5s sometimes.

Hey. I tried to post on that Acoustic forum where you have been spotted, but not having any luck. Is that site defunkt or somethin'?

[Boy Howdy]

I bet, OC D, that even your mighty fork would fail against these suckers. I bent two spoons trying to get these damn things loose.

[TomCarlos]

You scared me, Tom. And it ain't even Halloween. Those handwritten numbers are a pain on those ACC schems. You can't tell the difference between the 3s and the 5s sometimes.

Hey. I tried to post on that Acoustic forum where you have been spotted, but not having any luck. Is that site defunkt or somethin'?

I am unable to log into the "Tapatalk" site. This is probably the better site to be on.

[Boy Howdy]

I wanted to see if anyone there had any better pictures of the preamp board (ones where I could read the resistor values) since I couldn't remove the one from this 150. I haven't managed to find any that are clear enough.

[Boy Howdy]

Here's why I bought the 150, by the way. This is also a pic of the power amp board and where the 560 ohm R311 was/is located. Notice the golden brown color. Colonel Sanders could do no better.

I'm a big fan of Traut and Robby. As you can see Ross Traut used an Acoustic on their two CDs. It looked odd to me though. I finally decided that he had actually cut the head down from a two channel to a one channel, physically sawed away one third of the chassis! I emailed him and he confirmed that that is exactly what he did. He built the cabinet as well.

[TomCarlos]

Ya know, that is exactly what I thought about doing. I didn't need the extra preamp board and I too thought about borrowing my neighbor's saw. But in the end, I restored the amp and sold it to a guy who uses it daily.

I think the original intention of the 150 was to copy the Twin Reverb or that someone could use the other preamp board and purpose the 150 as a bass amp. Because if you look at the 136 / 140, it uses the same 17-10 preamp board (two of them) and the same Power Board One (17-12). One thing about the burning marks and solder points; make sure the traces and contact points to the holes have not been compromised. I use an Exacto knife to scratch away some of the protective coating so that when I solder a part, the solder flows onto the trace as well.

[Boy Howdy]

I certainly gave it some thought, but ultimately, given its age and the possible reliability issues of an old SS amp, and the age of myself and the unlikely possibility of me ever gigging again, I think I'll just leave it unmolested. Make it my go-to for tremolo sounds.