Express / SLO 50W hybrid

[bepone]

Starting one strange amp for my friend, to spend parts accumulated.. will be express with higher gain using unused tube half, and adding active fx loop (yes, yes, fx loop for delay and getting lead tones), master volume.. i wanted also bass cut control on roto switch but maybe in testing i will select only one cap.

Chassis from 18w (read short), some accumulated output transformers, many different and vintage components to try..

Looking at available resources..tried to follow original layout and lead dress but.. this will not be possible.. because chassis holes are not in right direction.. will be inverted.. then i redraw the amp on the paper and saw that KF lead dress cannot be followed.. Not possible because of rotation of the sockets.. then i started to thing more why is lead dress like that layed down. Maybe layout right to left, instead left to right and using different sockets wiring affect the tone?
Ofcourse but in this amp i will not find out.

[bepone]

So amp will have 2 cathode followers (before fx loop and after) which will make it very close to SLO territory and I can't wait how it will sound!

First 3 stages and PI will be TW express, voltage lower (400V ) to follow TW idea..

for EL34 OT i have several candidates , DIY Drake 784-139, 784-103, and now Orig 784-213 from Carsbro amp..i have hi permeability laminations and basic, will be compared to Carsbro.. maybe i will also wound 5k for TW amp who knows at the end.. we will see

[bepone]

Started with very boring job manually drill holes for turrets from paxolin predrilled board (3mm thickness) to empty textolite board (2mm) , turrets what i have are for 2mm , otherwise i will use first board..

IMG_20231118_153726.jpg

[bepone]

Turret board ready, found some vintage turrets for this project...

IMG_20231118_172241.jpg

IMG_20231118_172247.jpg

[bepone]

Turret board completed.. there is no too much free space in chassis, and i have 4 ECC83's, so more components..all squeezed on the turret board..

Material is mixed, starting with sozo/tad mustard combination, main core is carbon comp Draloric LCA's , but cathode followers MOX.. target is to have refreshing smooth sound full of gain, not too much bright.. Carbon comps/sozo/mox should be mix..but we will see.

IMG_20231120_223338.jpg

[Jered]

Looks good so far. Really interested in how this turns out. I to have lots of iron I need to put to work

[bepone]

thx , first sound will be somewhere next week..waiting PT which is expected on friday

[bepone]

Some progress..
Turret board in place, mounted OT, heaters connected, wiring to the socket pins done in TW style, all wires under 90 degrees or so to minimise coupling, added 2 more stages.. input to pin7 on V1 for minimum hum .
Need to find in drawers rest of the hardware these days

IMG_20231124_223608a.jpg

[Colossal]

Very nice layout, Bepone.

[bepone]

Very nice layout, Bepone.

thx, it's a bit crowded, but I'll try to compress all in 18w enclosure

[bepone]

Thinking of supply and how to install and available capacitors at home.. radial caps taking the least place .. but doesnt look like the rest .. so building optimised supply board according to dimensions of axials.. first cap 80uF is parallel of 47+33uF standard values.. found some F and T.. preparing the board for drilling

IMG_20231126_183834__01.jpg

[bepone]

ps board in progress.. 1k 25w resistor made from some smaller, drawers find

IMG_20231126_235544__01.jpg

[bepone]

wiring almost completed.. first powering on soon

12345.jpg

[bepone]

Complet of tubes available for this project, kt66s, ecc83s and 5751 which will be used maybe for v1 to tame some gain ..

IMG_20231202_223936__01.jpg

[bepone]

Amp is running, 2 days and tweaking in progress..

First start - orig express scheme and followers added (working in clean): excellent cleans (really excellent, present not harsh, a lot of sustain, ), but some fuzzy OD on gain pot on the way up to max, not nice, on low and high volume the same, checked on the scope, V2 is making from sinusiode with gain some sharp half wave triangle, clipping on one half only like it should do but for me this is not good tone
- maybe too punchy (2n2 from V1 to V2 cut too much bass?)
- on high volume harsheness increased
- not so much gain (?), just some medium crunch

I didnt try on high volume to get some OD from output, because amp will not be used like this, mostly on normal room/studio volume, and i think is wrong way, why some one need to became deaf for some OD?

Here is simple not so much tubes in preamp and cold clipper is not working for lower volume.
-----------------------
Modification started