members builds in progress

[LooseChange]

Funk, did you measure the total resistances at balance? I'm curious if it was the 82/100 ratio.
So slightly off balance was best. As you went further off did it seem to get harsh like 3rd order or just odd harmonics?

[Funkalicousgroove]

I used a 100K and a 110K, I'll try and get inside it and measure for you. It's not a huge difference either way, and it's not noticible until you kind of crank the amp past the point of distortion.

[llemtt]

The PI trimmer is there mainly to maximize the output power, you should watch on the scope and adjust to have the two halves of a sine wave clip symmetrical.

I found that even with 100k plate resistor and 20k trimmer sometimes you reach trimmer's range limit without a perfectly simmetrical clipping; swapping ouput tubes usually solves the problem.

[Icetech]

Mine in progress... i havn't put in the local feedback and stuff yet... wanted to not add more things to troubleshoot til i get it happy with the basics:)

http://mywebpages.comcast.net/roadrebel/odsr.jpg

Big pic.. dialup beware...

P.S. one wrong mouse click and i have radial cathodes caps.. kinda like em standing around though:)

[llemtt]

If you want to balance the PI not having the (power amp) feedback loop in place is even better because the loop tend to reduce any imbalance!

[Normster]

Mine in progress... i havn't put in the local feedback and stuff yet... wanted to not add more things to troubleshoot til i get it happy with the basics:)

http://mywebpages.comcast.net/roadrebel/odsr.jpg

Big pic.. dialup beware...

P.S. one wrong mouse click and i have radial cathodes caps.. kinda like em standing around though:)

Looking good, man! I think the Bassman chassis is a great platform for building a Dumble. One minor thing I noticed that you might want to swap out. It looks like you used 1 watt 5% carbon films for your power tube cathode to ground. You'll get a more accurate bias reading if you use 1% resistors.

[groovtubin]

I s'pose you have all seen these, but I thought I'd post them here anyway. This one is an EL34 amp and uses a Heyboer Marshall PT, an OEI OT (Friggin superb by the way!!) and a Pacific Twin-reverb style choke. It basically follows the 1997 schematic that Dogears posted. I used a combination of 225p and 715 Orange drops in spots where I wanted a bit more top end.

I

[Funkalicousgroove]

That amp is very very "Pristine" clean, all my friends say it sounds "Transparent" it's definitely not thin or harsh sounding. The OD on this one sounds like Later RF, it's much lower gain than the non-HRM amp that I personally play, but I plan to build another just like it for myself at some point.

[groovtubin]

That amp is very very "Pristine" clean, all my friends say it sounds "Transparent" it's definitely not thin or harsh sounding. The OD on this one sounds like Later RF, it's much lower gain than the non-HRM amp that I personally play, but I plan to build another just like it for myself at some point.

[dobbhill]

[quote="Funkalicousgroove"]I used a 100K and a 110K, I'll try and get inside it and measure for you. It's not a huge difference either way, and it's not noticible until you kind of crank the amp past the point of distortion.[/quote]

FYI:
The ODS I measured had a 91k and a 110k.

D

[Funkalicousgroove]

FWIW I also used a 5751 PI for max clean headroom, I didn't want the clean side to break up. 100K and 110K is what I had at hand, I've also built them with 82K and 100K, and 2 100K's it makes little to no difference.

As far as being "Thick and chocolatey" My Non Hrm amp is Liquid Magma, this one is different, it has EL34's and a Post OD Tonestack, it's more crunchy- it sounds more like Sonny Landreth or Jing Chi, it's a Fantastic amp, I hated to turn loose of it!

[groovtubin]

FWIW I also used a 5751 PI for max clean headroom, I didn't want the clean side to break up. 100K and 110K is what I had at hand, I've also built them with 82K and 100K, and 2 100K's it makes little to no difference.

As far as being "Thick and chocolatey" My Non Hrm amp is Liquid Magma, this one is different, it has EL34's and a Post OD Tonestack, it's more crunchy- it sounds more like Sonny Landreth or Jing Chi, it's a Fantastic amp, I hated to turn loose of it!

[groovtubin]

FWIW I also used a 5751 PI for max clean headroom, I didn't want the clean side to break up. 100K and 110K is what I had at hand, I've also built them with 82K and 100K, and 2 100K's it makes little to no difference.

As far as being "Thick and chocolatey" My Non Hrm amp is Liquid Magma, this one is different, it has EL34's and a Post OD Tonestack, it's more crunchy- it sounds more like Sonny Landreth or Jing Chi, it's a Fantastic amp, I hated to turn loose of it!

[jazzyjoepass]

Thanks Normster, It' a Bangkok. The pedal switch on the front panel swithes Pre/Post tone stack. Had to mod a couple of concentric pots for my needs..100K A/1m A---100K A/250K A. Wanted to see if I liked the PTS or not. I,m sure it could be switched with a relay.. Would be a nice double edge lead as you can control the volume and drive of each. I had also added two more power tubes to run a quad of JJ 6v6's with Pent/ Tri switch and a half power switch on outer tubes.

I'm inspired by you do do the same!!!

Could you share how you modded the concentric pots?

[toneman]

The Secret Life of Pots by RG Keen could explain it better. Had changed the wipers to what I needed. It worked great so I went a step further and added a relay instead of the panel switch.