The 6550 Experience

His guitar slung across his back, his dusty boots is his cadillac.

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Frank1969
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Re: The 6550 Experience

Post by Frank1969 » Fri Jul 31, 2020 12:10 pm

EL34 JJ
and E83CC TESLA

revolver1
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Re: The 6550 Experience

Post by revolver1 » Thu Aug 06, 2020 4:36 am

Got a chance to do some more experimenting. First I tried the .0047uf on V1b plate bypass and a 3uf on V2a cathode and there is way, way too much gain here.

I then went to .0068uf on V1b and 2.2uf on V2a and in my amp this was much, much better. The drive was more balanced and useable and cleaned up off the guitar volume. I do think it sounds good but I'm still not 100% sure I'm sold on the V2a cap. The gain lift is nice but it does sort of focus the sound and misses some of the harmonic content and overtones you get without it.
With out it there is definitely more of the older open Plexi sound there, it sounds more woody and natural to me.

So I'm back to just the .0047uf on V1b with no cathode bypass, the more I play it the more it sounds right in my amp st least.
There was something going on with the wah that sounded right back when I had the .0022uf in there but for the rest the. 0047 is doing it for me.

This leads me to my next trial. Shakti brought this up way back and I had been thinking it myself to daisy chain a West Coast into a stock 69.

The other thing I didn't try and I probably need to rule out was a .022uf on V1b and a 1uf or 2.2uf on V2a. I can't help thinking any mods probably would have been done with typical values lying around the work shop for amp repair.

daveweyer
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Re: The 6550 Experience

Post by daveweyer » Thu Aug 06, 2020 4:09 pm

Why not just share the cathodes on V1, and get the gain and treble boost you want on V2-A cathode, if needed?

revolver1
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Re: The 6550 Experience

Post by revolver1 » Fri Aug 07, 2020 10:04 am

Hi Dave,

Yeah it is shared cathode on V1 so that's exactly what I've been playing with.

I think I'm really quite happy with the .0047uf instead of the .0022uf and no bypass cap on V2, it does sound really cool and alot more versatile than when I first built it.

Messing around playing power to soul the overtones are just right.

I think next is to play it in a bigger space and I really need to get a Stratocaster. I'd been after a 65 ARVI, They are discontinued now so I have to wait for one to come up on the second hand market. Trouble is people don't want to sell the good ones. Most of the ones I've seen seem to have slight issues or I just don't like the colour. The only other route now is the Custom Shop line that's just come out but I need prices to cool off a bit first.

Besides with the lack of my desired Strat I fell victim to the Zemaitis end of line blow out and picked up a Custom Shop metal front. That will have to do me for now unless I like the idea of divorce :lol:

I think with the Strat the amp may need the slight gain lift, maybe not but if it does I think the 2.2uf will be the ticket.

So the mods I've done are pretty much along the lines of everyone else with the exception that my amp is a 50w.

467vdc on the plates.
Real Tungsol nos 6550 biased @ 25.1ma and 25.4ma
2.2k 10watt screen resistors
Mullard nos 12at7 in V3
Filtering has been modified to 100w format;
2x 100uf mains
2x 50uf screens
1x 50uf Phase Inverter
1x 32uf Pre Amp
Shared cathode - I put a high reading carbon comp on V1 cathode that came in around 880 Ohms if I remember right. This helped smooth out the slightly harsh drive i was hearing.
500pf / 33k tone stack. Tone stack, mixer and P.I caps on the board are all mica.
4700pf bright cap on the Vol pot.

I think the only deviations I did differently from anyone else were:
15k on the Phase inverter tail resistor
.0047uf on V2 coupler instead of stock the .0022uf
And no cathode cap on V2

I think that was about it.

Using an Analogman Silicon BC183 fuzz Vol 10 Fuzz 3ish into a Scumback H55hz and an H75hz.
Also using an mjm Uni Vibe wich definatly helps leaving it in the chain when not actually engaged.
And a BMF Clyde McCoy clone mostly because it has a buffer to place it before the fuzz but I also have a Castledine McCoy but that is un buffered and I don't really want to mess with it. Sounds great with out the fuzz though.

:thumbsup:

revolver1
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Re: The 6550 Experience

Post by revolver1 » Fri Aug 07, 2020 10:16 am

Oh yeah, also using settings as suggested:

Into high input 1

Pres 9
Bass 4
Mid 6
Treb 4
Gain 1 7
Gain 2 turned up around 7 to 8 to thicken it up.

My neighbour's love me... :toast:

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