Dumble - help needed urgently!

[Aaron]

I've figured it out, Martin Manning is..........Brown Note!!!

Nice work Martin. And at 10:1 odds you made me a lot of money.

Mousey, glad the amp has worked out for you.

Aaron.

P.S:- rest up Martin, I can see a JM build after the tour.

[Mousey Dung]

The reverb tank is an antenna for the EM field from the PT, just like the OT is. Position the reverb tank while the amp is in operation. You will be able to hear the hum increase and decrease as you move the tank in relation to the PT.

You made me think of something else. I made a mistake when building the combo and as a result, the OT is pretty close to the speaker. Does this have any bearing on the output or hum factor?

[xtian]

Does this have any bearing on the output or hum factor?

Have seen this question many times. No one seems to think it's a problem.

[martin manning]

Only one way to find out, but lots of combos are pretty tight. How are you going to mount this reverb tank in a combo cab?

PS I guess the write up uses the term "on end" for what I was calling "vertical."

[Mousey Dung]

Only one way to find out, but lots of combos are pretty tight. How are you going to mount this reverb tank in a combo cab?

No noticeable increase in hum. Just hope it's not sucking any signal or tone.
I have some horizontal back boards that I could put the tank behind, but the tanks won't be flush against the board and will be open on both sides lengthwise, with a 3/4 inch gap.

PS I guess the write up uses the term "on end" for what I was calling "vertical."

I did figure that out

[martin manning]

BTW, 9FB2A1C reverb unit has 1925 ohm input impedance. Is that the recommended part number? What is the output impedance of the reverb driver transformer you have in this amp?

[Mousey Dung]

BTW, 9FB2A1C reverb unit has 1925 ohm input impedance. Is that the recommended part number? What is the output impedance of the reverb driver transformer you have in this amp?

Leaving for the train now ... I brought some tools and my laptop. Will check RT output impedance later... Thanks so much for still thinking about my build, Martin!

[xtian]

Extra points for photos from the road. Rock on, mouseman!

[martin manning]

Hey Chairman, looking at the chassis picture you posted earlier I can make out the number 22921 on the top of the reverb transformer. That tells me it is probably the standard Fender type which has an 8 ohm output. I suggest picking up a new reverb tank such as 9AB2A1B, which has 10 ohm input impedance and mounts open side down (better for a combo cab; you can put it on the bottom in a bag). That will get your 'verb on.

[Mousey Dung]

Hey Chairman, looking at the chassis picture you posted earlier I can make out the number 22921 on the top of the reverb transformer. That tells me it is probably the standard Fender type which has an 8 ohm output. I suggest picking up a new reverb tank such as 9AB2A1B, which has 10 ohm input impedance and mounts open side down (better for a combo cab; you can put it on the bottom in a bag). That will get your 'verb on.

I'll have to look into that for sure. The reverb is there, but very soft. All that happens when I dial in more of it is what seems to be longer duration reverb, but just as soft.

[martin manning]

That makes sense. With such a huge impedance miss-match, the reverb driver is going to have a hard time getting any energy into the springs.

[Mousey Dung]

Hi Everyone!

The amp's mostly been holding up just fine. The footswitch for the middle boost malfunctions on occasion. I haven't had the time to swap wires with one of the other switches in the three-switch unit to ascertain that it is the switch itself that is faulty. Perhaps its the relay or something else... the middle-boost switch doesn't do much when I flip it on, either manually or using the footswitch. There's barely any discernible difference. Perhaps the problems are related somehow?

Apart from that, I really like the tone of the amp.

Before I left, I had spent many hours tweaking the OD and PAB to get some rich tones, then I put the chassis back into the cab and left it alone. On the first night of the tour, my solos just weren't cutting through. The OD tone was not quite like I thought I had set it -- it was muddy and subdued. Although I'm aware that a lone guitar amp sounds quite different than when it's next to a host of other loud instruments, I also figured that the tone of a disembodied amp is probably appreciably different than when it's sitting in the cab. So I pulled out the chassis again to test my theory. Sure enough, the tones were all there again, no muddiness, no lack of umph. I added more treble and middle than my ears would have preferred, turned the PAB hi-pass cut down to zero (no cut), reattached the chassis to the cabinet, and as expected, everything was as it should be without the middle/high compensation: there was warmth yet definition, screaming rich harmonics/ overtones and feedback in all the right places. I was also able to get some transparent and edgy blues tones and somewhat Carltonesque sweet mid-range tones just by dialing in some different knob settings.

[Mousey Dung]

Extra points for photos from the road. Rock on, mouseman!

I have an unfavorable endorsement deal that I'm trying to get out of, so I can't be caught on camera with a different amp just yet. Really silly, but over the years, I've discovered that I don't really like their products anymore.

[martin manning]

Glad to hear it's (mostly) working out! You should hear a pretty big difference when the mid boost is engaged, so something is probably not right there. When you get a chance, see if you can confirm that the Mid Boost relay is switching when it's engaged by checking for continuity from common to the NO (normally open) contacts when it's on. Do that with the standby off, just to be safe.

BTW, what speaker are you running?

[Mousey Dung]

Glad to hear it's (mostly) working out! You should hear a pretty big difference when the mid boost is engaged, so something is probably not right there. When you get a chance, see if you can confirm that the Mid Boost relay is switching when it's engaged by checking for continuity from common to the NO (normally open) contacts when it's on. Do that with the standby off, just to be safe.

BTW, what speaker are you running?

In the composite image below, the top part is the wiring as shown in the diagram. The bottom part is my wiring in red. Do I check for continuity between points 1 and 2 to determine with there is continuity from common to N.O.?