Everything You Ever Wanted to Know: Pictures & Diagrams

[fabiomayo]

A little late as I've been away for quite a while:

THANK YOU!

[paddy]

Gil,



Interesting also the values for the pots. I don't recall seeing a non-HRM guideline that has 250KL as the Drive pot. Maybe I'm just confused...

Thanks again!
Michael

4. Ditto on the mix'n match pot thing. Seems like a transitional amp that eventually led to the 90s design.

Gil

Hey guys
just interested to know how you decided the drive pot is linear?
according to this site
zeus.lunarpages.com/~jimshi2/potcodes/potcodes.htm
the pot code is for audio taper.
of course I could be staring at the wrong pot--eye strain from looking
at all those wonderful photo's!

Cheers
Paddy

[ayan]

Gil,

just interested to know how you decided the drive pot is linear?
according to this site
zeus.lunarpages.com/~jimshi2/potcodes/potcodes.htm
the pot code is for audio taper.
of course I could be staring at the wrong pot--eye strain from looking
at all those wonderful photo's!

Cheers
Paddy

Paddy, you are correct. In my original post I said the taper wasn't recorded on my friend's notes and the amp got so gainy so suddenly, that I thought the pot would be linear. However, we know the Treble pot is linear and it's an "Alpha" while the middle pot is audio and it's a "CTS." Looking carefully at pictures like #82 and #83 of the set, it's plain to see that the "Level" pot is also a CTS and of the same code as the midrange pot, and therefore it must be audio taper. I will also make a guess: bet you the new Middle and Level pots are the old Treble and Bass pots, since the latter used to be 250K audio in the early 80s amps.

Cheers,

Gil

[paddy]

Thanks for clearing that up Gil,your assumptions regarding the other pots seem to be correct IMO.
I do have a quick question for you if you can spare the time.
I have configured my amp using as many of the new values as possible.
I'm only a novice guitarist so I had a few local pro's check it out and they are all in agreeance that the amp is fantastic.The only critisism is that the clean channel just starts to break up with the volume control at 4.
Is this the same with Billy's amp or all Dumbles for that matter?
None of us have ever played a Dumble in this neck of the woods.We kind of expected it to be Fender clean although i realize Fender place the tone stack after a cathode follower(in the Bassman that is).
The guitars used for testing were Les Paul,335 and Ibanez SZ320.

Many thanks for any help
Cheers
Paddy

[llemtt]

I will also make a guess: bet you the new Middle and Level pots are the old Treble and Bass pots, since the latter used to be 250K audio in the early 80s amps.

Makes sense, although HAD claimed to carefully select components actually sometimes he used everything under hand...



teo

[ayan]

The only critisism is that the clean channel just starts to break up with the volume control at 4.
Is this the same with Billy's amp or all Dumbles for that matter?

Paddy, I take it you mean with the preamp volume control at about 4? Then, we'd have to determine whether you're using CTS 10% taper pots, or Alphas which can be more like 15% taper, or vintage CTS pots which can be more like 30% taper. So, if it's preamp breakup we're talking about, we also need to consider whether you have the old style feedback around V1B, i.e., 20 Meg + cap, or the later style feedback with 40 Meg + cap, or no feedback at all as in the HRM amps. The less negative feedback, the more gain available on the clean channel.

It's been my experience that these amps don't really break up on the clean channel until you get the power section going a little bit. However, in Billy's amp's case, it does break up more than usual in clean mode, which I attribute to its old electrolytic caps. In all cases, adding the preamp boost on top of the clean chanel will make it grind a bit, even if the power section is running totally clean. In Billy's amp case, clean + PAB = singing overdrive.

Don't know whether this helps, I hope it does.

Gil

[paddy]

Hi Gil,
Thanks once again for the info.
Well it seems as if I'm a lucky boy,as my amp seems to behave quite
similarly to Billy's.Bit of a waste on a beginner like myself but I will improve with time and practice.
The vol pot is CTS 10% taper and I'm using 44Meg on CL2.
As you described,the amp does stay clean untill I wind up the master
a bit and if i set the master to the point where the amp is clean again,it only takes a small adjustment of the vol pot to get it to break up again.Quite nice really.
I have 2 x 22meg resistors in series for the CL2 feedback loop and shorting one of these out does clean things up a little
Thanks for the help
Cheers
Paddy

['67_Plexi]

Anybody figure out the efx send / return set up on this ? The cap and resistor in parallel between the sockets threw me. Why would there be frequency manipulation at theat point ? It's still obviously designed to be run with an external efx loop processor such as the Dumbleator with an RMS signal of 2.5V.

[ayan]

Anybody figure out the efx send / return set up on this ? The cap and resistor in parallel between the sockets threw me. Why would there be frequency manipulation at theat point ? It's still obviously designed to be run with an external efx loop processor such as the Dumbleator with an RMS signal of 2.5V.

The little resistor and cap in parallel are connected to the switching lug of the return loop jack. So, when the loop is used, the network is out of the picture all together. I did hear the amp as is, VS patched with a short cord in the loop... and noticed that the network adds a little bit of treble to the sound of the amp. When using a Dumbleator, you get a choice of two bright switches on it, so I guess Dumble figured the owner didn't need a permanent brightness network all the time.

Gil

['67_Plexi]

Just a heads up and word of warning to avoid smoke and exploding caps....the handwritten drawing of the voltage doubler psu for the relays is incorrect. As drawn for 1/2 of the cycle the diode will rectify inversely to the polarity of the capacitor and we all know what happens when you connect an electrolytic up the wrong way around.

Here is a correct drawing of a voltage doubler, hope this helps.

[keithrick]

I have been converting my amp to the #124 specs using the pics provided by the Most Excellent, Gil and Billy when I noticed that V1 PIN 1 is facing the back of the amp. Well what could this mean???

Look at these pics below!

1. The 500pf bypass cap bypasses the 22K input cap.

and that

2. Negative feedback is applied to the input side of V1a not V1b and it also looks like there are (4) 10 meg reistors two on each side of the cap.

Why is this important? This is the opposite of everything I have seen on the internet!

Please tell me I'm crazy. I used my trusty resistor code calculator to check values but I could be sure of some of the bands colors. I have been huffing solder fumes all day so if I'm am wrong please no flames!

[tonelab2]

The blue heater wire = pin 4/5
Red heater wire = pin 9

[tonelab2]

Please tell me I'm crazy.

O.k. your crazy

[keithrick]

Maybe, (front picture) Look at V2 it looks like the RED wire is pins 4+5 bent together and soldered. Then look at V1, by the blue wire is the gap between pin 9 and 1.

I know I need some fresh air huh?

[paddy]

Hi Keithrick

Looks to me like the red wires go to pin 9 and the blues go to 4/5.

Cheers
Paddy