#0124 Again

[ampdoc1]

Revised for easier downloads 10/18/06

A member alerted me that this schematic had gone missing. i had to do another small change (a missing wire on the "boost" switch), so I revised the drawing and reposted it. Also included is my d-mbl- component spread sheet.

[Normster]

Excellent! Were you able to verify how the half power switching works?

[jelle]

Hi,

I can't open the files...am I the only one with this problem?

Thanks,
Jelle

[v00d00blues79]

I was able to open the schem, but the excel file is not there.


Thanks,

Andy

[jaysg]

I couldn't open it, but I could right click and Save Target As... Using Save Picture only saved the thumbnail.

[d95err]

The picture doesn't work because the filename ("D-mbl- #124 rev2.gif") has several characters that are illegal in a URL. For instance the '#' and space. Some browsers may support this, some won't.

It is always a good idea to avoid spaces and special characters in filenames when posting something on the web.

[jelle]

I managed to save the schematic on another computer. Nice drawing!
Thanks,
Jelle

[ic-racer]

This #124 schematic was originally posted by ampdoc1 and I did some fine-tuning to make it match the original amplifier.

DISCLAIMER: This schematic is pesented as a historical document for the benefit of those researching Dumble amplifiers. Since I did not create this schematic and I have no personal experience with #124, all the information contained herein was obtained from internet sources, so use at your own risk.

The relay switching items are still not included.

NOTE: Most recent update to this schematic was 1/6/08. However a more complete version can be found at this link:https://tubeamparchive.com/viewtopic.php?t=4354

[JimiB]

I can't open either of these.

[Structo]

me too, err neither.
I think it is a problem with the GIF image, My PC doesn't like me to click on those.
Bells start ringing, lights start flashing.....

[heisthl]

I'm guessing the 2 Amp fuse is a mistake - probably more like 5 amp.

[ic-racer]

I added a much smaller jpeg, see if that downloads.

[ic-racer]

I'm guessing the 2 Amp fuse is a mistake - probably more like 5 amp.

Good pickup. I checked the #124 back panel picture and Mr D asks for a 3 amp fuse.

Of course Duhh... now that I see this I remember that I forgot the 50/100 switch circuit....

...and I forgot to label the 'Ratio' rheostat...

[dogears]

OD pots are reversed. 100K is the ratio. The level pot is 250k and is the one that is in series with the .01uf V2a cap.

Also, I'd mod the schematic to reflect the 350K trimmer. Not an asterisk. Too important to get wrong. There is some question as to whether the resistor feeding it is a 120K or 220K. Gil tells me 220K, but the pictures are inconclusive and Billy says 120K. My ears say 120K if that trimmer is so big as well. I'd probably spec a 250K trimmer with 220K resistor. Fwiw, this yields about the same net impedence as the later HRM amps when factoring in the parallel loading of the clean master.

Lastly, the bypass cap on the V1b grid is 500pf. There is a difference from 470pf to 500pf....

[ic-racer]

OD pots are reversed. 100K is the ratio. The level pot is 250k and is the one that is in series with the .01uf V2a cap.

Also, I'd mod the schematic to reflect the 350K trimmer. Not an asterisk. Too important to get wrong. There is some question as to whether the resistor feeding it is a 120K or 220K. Gil tells me 220K, but the pictures are inconclusive and Billy says 120K. My ears say 120K if that trimmer is so big as well. I'd probably spec a 250K trimmer with 220K resistor. Fwiw, this yields about the same net impedence as the later HRM amps when factoring in the parallel loading of the clean master.

Lastly, the bypass cap on the V1b grid is 500pf. There is a difference from 470pf to 500pf....

Excellent, thank you!