Trying to build a Mesa Boogie V-Twin Pedal

[dinosaur]

I'm trying to build this pedal from the schematic found at http://www.tubefreak.com/mesa.htm#vtwin. 

However, there is no part list, and  I don't know what to choose for LDR (Light Dependent Resistor)

Someone can help me ?

[Johan]

those LDR's are only for channekswitching..I think Mesa uses vactrol vtl5c10, but nor sure...you can replace them with a regular switch or a relay..

johan

[dinosaur]

Thanks a lot Johan.

By the way, do you know the nominal value for V+, the tube's plate Voltage ?

[Johan]

Thanks a lot Johan.

By the way, do you know the nominal value for V+, the tube's plate Voltage ?

..no I dont...but looking at the schematic, the first cap at the V+ is rated at 350v, witch is probably high enough to accept a little variation in inputvoltage. then you have 3 x 4,7k drop resistors and finaly it feeds 4 tubestages. if we guess 2ma for each stage ( wich is just a guess but not unusal value ..)..thats 8ma droping over 15k roughly..voltage drop 120volt ( 8ma x 15000ohm ) from 350volt gives 230volt..if the first cap is overrated 10% I would say that the V+ should be somewhere around 200volt...but thats just a guess..

johan

[Johan]

..and now I noticed that transformer T1 says 1:18 and input 12vac thats 216volt ac or 302volt when rectified..with that voltagedrop over the resistors you have 180volt...
johan

[nelson]

A layout for this pedal would be more than awesome.

The prices these things fetch are pretty ludicrious for a tube stompbox preamp.


Keep us updated!

[macula56]

not meaning to hijack, but i have one in the for sale section.

[electrictabs]

...just a thought that someone told a long time ago and now i'am really happy he did...
why immitate?
why won't you innovate?
well since you're gonna mess with high voltage why won't you build something full tube that will sound even better than v-twin
you can use the same trannies that you would use with the v-twin and with hard-wire switching you can even make it for less money...
with 2x12AX7 and appropriate channel switching you can have a really nice clean sound and a great overdrive-distortion sound
(with 4 gain stages you can easily get to hard-rock/metal territory)



Johan in my tube preamps (with the specific tranny arangement) i use 1k/47uf filtering that does the same filtering job with 4k7/10uF but puts almost 240-250V.

[dinosaur]

That was my intention. I don't want to build exactly what's on this schematic because

- power supply section will be a  recycled one (instead of the wall wart AC Power Supply + the internal pedal power supply section)
- I think there are mismatches between channel switching control section on the bottom of the schematic and the analog preamp part (from my point of view, the Qi controlling the Gates of most J175 FET are not compliant with the mode/bypass/clean/blues switches as described in the user manual  and they have been wrongly indexed).
- I'm not an expert in tube

The upper part of the preamp section looks like a classic McTube preamp design (as can be found on Fred Nachbaur's Vacuum Tube Projects web site, http://www.dogstar.dantimax.dk/tubestuf/), and the lower part to other classic preamp design. I'll first try both of them as is on the scheme, and will certainly adjust/adapt/modify parts the way my ears will appreciate the result.

[Johan]

Johan in my tube preamps (with the specific tranny arangement) i use 1k/47uf filtering that does the same filtering job with 4k7/10uF but puts almost 240-250V.

...there are ways to calculate these things, but much to complex for my tiny brain, so...I was once told to estimate about 10uF for each mA currentdraw, when selecting filtercaps..and that has served me well, so...with 4 stages pulling about 2mA each, I would use 80-100uF..

johan