Another Dumble style amplifier

[Richard1001]

Hi,

My name is Richard, I'm from Holland and have been reading on this forum for some time now. With information found here on this site and elsewhere on the internet I build a Dumble style clone in a Marshall like case. I thougt it would be nice to share my experience with the members on this Forum. My clone is somewhat different than the designs i saw most on the net, but the result is ok I think.

Here are some technical notes:

I do not use a JFET input but instead have a normal (triode) and a Penthode input, using a EF86. The EF86 has 2 times the amplification factor of the standard triode input, so it's like having a high and a low input. There is also room for tube rectifiers, tough I don't have these yet.

I use the older values for the tone stack pots, caps and resistors. (250K, 100K, 250K, 0.047uF for mids en a 100K tone stack resistor. I use 2 caps on the bass pot (I saw this somewhere) so you get a real braxandall tone circuit when switshed to 'jazz'

All pF caps are SM except on the pre OD network. This network is somewhat different than what I saw in other designs and compensates high frequenties when the gain is turned up. (and enhances them when turned down)

For output tubes I use 6550's and the feedback circuit is 3k9 / 390 ohm on the 4 ohm tab.

I have a little clip on youtube recorded whit my cellphone. The EF86 input is used and the speakers are G12-65's:

http://www.youtube.com/watch?v=SdzCtNRT ... re=related

hope you like it....

[El_Martin]

Hi Richard!

Looks and sounds nice or shall I say lekker ?

This one ventures a bit more into Marshall territory, soundwise.

Like it

I think, there should be more rock sound snippets of Dumble variants...
Just to enlarge variety.

Ciao
Martin

[Bob-I]

Wow, that's a great amp. I agree with Martin, it's more Marshall than Dumble but it sounds and looks great.

[Tonegeek]

These amps can be made to do it all. I like it! Would love to see your schematic...

[Normster]

Your amp looks and sounds great! Also, smokin' solo on the AC/DC clip.

[skyboltone]

Very nice indeed. How do you manage the patience to cut in those slide switches. All of the early Dumbles had them.

[benoit]

Very nice indeed. How do you manage the patience to cut in those slide switches. All of the early Dumbles had them.

Doesn't look like these are done this way but I'd think you could just do a round hole and then do a square hole in just the faceplate, if you were using one. Also someone talked about a mechanical vibrating file, that'd probably work great if you drilled a round hole first and had your hole marked out.

[Richard1001]

Thanks, it's nice to hear you like the sound.

I did not have the patience to cut the slide switshes, I had the chassis made to my specifications. It's laser cut.

As soon as I have the time i will draw and post a schematic. All I have now is lot's of paper with different drawings, none of them realy correct.

[ampexplorer]

Hello to all, great amp and sound. I have also been thinking of using a larger chassis like a twin or SLO when I get around to doing my build. Very nice work Richard!!

[benoit]

Hello to all, great amp and sound. I have also been thinking of using a larger chassis like a twin or SLO when I get around to doing my build. Very nice work Richard!!

If so you should check out the recent thread where someone was doing the same thing. Someone posted a faceplate template that will fit a twin chassis perfectly. If you've seen it, cool, if not, here it is: https://tubeamparchive.com/viewtopic.php?t=4773&start=0