Vadis To Dumble #183

[TIMBO]

Hi guys, Looking for something to do :eyeroll
I have had a Vadis four input 60w PA on the shelf for sometime now so it's time to PIMP my amp.
I had not even opened it up to see it's guts, but now that I have it's originality is long gone.
Lots of holes in the front panel, three peramp sockets on the upper chassis and phase inverter power tubes on the lower.
Power transformer is not original and the A&R if the model number is correct(faded of sticker but the last three numbers 892) the only PT that I can find with those numbers is a 1892.
The rectified volts are about right for a pair of EL34 @60w but the mAs are a bit low.
I have not built a Dumble so this should be fun

[tubenit]

I will be following this with great interest!  Should be a fun build to attempt.

My understanding is that layout is critically important for the Dumble tone. Having said that, I certainly think it's possible to
have a good layout without following the Dumble layout.  I don't know of anyone who built one with a split chassis, but I don't see why one couldn't do that successfully?

I have found orientation of the caps to be significant in reducing noise in my dumblish inspired amps, so I'd recommend taking the time to do that.

With respect, Tubenit

[TIMBO]

Thanks mate, I have not done the cap orientation thing before, but will do with this one.
The chassis are from a head cab, so wire runs will be short.
 

[TIMBO]

Hi guys, After much thinking I've worked out how I'll do this...

Chassis striped and cleaned

Lots of holes to work with.

Need to get some parts in.

[TIMBO]

Hi guys, A little progress..

[tubenit]

Looking good!   

Thanks for sharing this build thread!  Looking forward to your review of the amp and maybe a sound clip or YouTube.

With respect, Tubenit

[TIMBO]

Relays in

[TIMBO]

Hi guys, I bought some reverb boards off Tristin Collins some time a go,so I'm keen to see how they perform
I don't fully understand how they are grafted into the circuit...

[TIMBO]

Hi guys, I hate it when work slows the solder fumes.

[tubenit]

Timbo,

Do you have a schematic with this, please?  I am understanding that you have a split chassis thing going on with preamp in one and the power amp in another?  Is this correct?

with respect, Tubenit

[TIMBO]

Hi T, Exactly


Work is slow on this one.

[TIMBO]

So a mate is looking for a DUMBLE




Wiring completed
The reverb was removed
Foot switchable PAB removed

[tubenit]

Cool project!  Thanks for sharing.


With respect, Tubenit

[TIMBO]

Hey guys,
A bit of time in the shed between the feasting and family stuff.
Got a few bugs sorted and sounding good.

The replacement PT is only putting out 330v at Node "A" which is probably around 30w output 
I'll tart up the head cab and possible build a 2x12 matching cab

[tubenit]

I love this project!!       Thanks for sharing!  Somewhere down the line IF possible and convenient, I'd love to hear some sound clips of this amp even if just recorded with a cell phone. 


This has been a really innovative project.



With respect, Tubenit

[TIMBO]

Thanks T.
The Dumble's really have a different sound.
The overdrive is so smooth with lots of sustain and bark when you dig in.
My stunt guitarist loves them so I don't think it will be too hard to convince him to do a clip.


So far there is no excessive noise or hum due to the split chassis

[shooter]

stunt guitarist

meters n scopes are a techs tool box, but add in a stunt guitarist and you stand above the rest!

[TIMBO]

Hey guys,
I've got a problem
All was working well till the power tubes started to redplate.
Back on the bench and ...
Negative bias has a good range and is present at pin5 on the tubes socket
1ohm sence resistor connected to pins 1 and 8


Bias was set at -22 with approx. 70mAs at the 1ohm resistors and 330v at the plates, then within seconds the mAs rise to over 110mAs and the tubes start to redplate
Adjusting the bias has no effect on the rising mAs


This is a first for me 

[TIMBO]

Hey guys, I may have rumped the gun on this one.
Chucked another set of tubes in and all is stable

[bmccowan]

"rumped the gun" Timbo, is that one of those odd Aussie slangs?

[shooter]

it's all that SUN he's enjoying, twitches the qwerty fingers


Make sure it's stable on the bench a couple hours


a shorted tube will mess up the bias, but so will a sketchy connection so bump it a few times while it's on the bench

[TIMBO]

"rumped the gun" Timbo, is that one of those odd Aussie slangs?

Some more here
100 Most Common Australian Slang Words and Sayings

[TIMBO]

Hey guys
A few tolex repairs done to the head cab and put back together.
A faceplate will de designed


Speaker cab constructed and sanded ready for some tolex


I'll use these, made in the early seventies and has been said they sound similar to the greenback
The Etone brand speakers were used by many of the local builders at the time.


Great condition for 50+ years