YMI's 12xxxx build - feedback please

[YMI5150?]

Here are gut shots of my build as it sits now. It sounds pretty damn good. Any suggestions based on what you see that might improve things?

Here's a clip at 90 volts

http://www.soundclick.com/player/single ... i&newref=1" onclick="window.open(this.href);return false;

I'm using an external variac so I want to get rid of the 3 position switch.
B+ voltage at 120 VAC input is ~ 440VDC. B+ at 90VAC was 344VDC or so. I dont have bias data here now but will get it. audible feedback from others (and I concur) was it sounded like it was too cold. I turned input voltage to 95VAC and it sounded much better.

I have the Marstran -132 OT and it seems a bit dark to me, very much like Fair Warning and 1984 tone. not a bad thing but not quite early VH. 4 ohm 100k NFB, selector on 8 ohms.

I'll post a clip tonight of the current setup.

IMG_1574 forum.jpg (130.52 KiB) Viewed 4993 times

IMG_1577 forum.jpg (112.14 KiB) Viewed 4993 times

IMG_1578 forum.jpg (87.48 KiB) Viewed 4993 times

[vanhalen5150]

Whats the resistor on pin2 V3?

[YMI5150?]

If you recall a PM from VHJunkie back when we were all wrapping up our builds. it was a solution he suggested to eliminate a cymbol crash sound common with these builds. I can remove and compare.

I should have posted the slaved clip because that's my setup at home. The clip above was attenuated with a 1 wire mod PB. I have a Hot Plate at home and its not nearly as good. fine for line load though...

[vh junkie]

My 69 build had that same dark sound with the 132 tranny. I tried avery way a could to jettison bass early in the signal chain to no avail. Turned out it was the damn F&T 32/32 preamp can! I replaced it with an ARS and the darkness cleared! 32/32 axials are hard to come by (vintage $25 Eries are available but need to be specially formed first!). You can try two of the 16uf TADs (look at Georges 12xxx, also notice he doesn't let F&T caps anywhere near the preamp on his builds!)

[YMI5150?]

strat78 has already mentioned the need for Merr...PT and 2.2k OT. I have to say that if i could lift the rug off this Marstran 132 I'd probably call it about good. the low B+ concerns me as well as low heater voltages when variac'd below 100vac. maybe the merr.. PT would cure that. but not sure how that affects tone. i would like to go (or be able to go) from a Fair Warning sort of dark heavy tone to a VH II tone. I think the difference between VHI and II is a slave setup and a pickup. same plexi. Junkie - any reason to try lifting that cymbol resistor?

I'll look for a new preamp filter. thx for that. I'm all about cheap fixes first.

[vanhalen5150]

Yeah I remember the cymbal crash but have never heard what people mean by that. What value was that resistor?

[YMI5150?]

the resistor looked like a 220k. is that right Robert? red, red, yellow. I'm going to pull it when I throw that preamp filter in and see if it needs to be there. wonder if it robs sizzle while taming cymbol crash.

[YMI5150?]

Ok, swapped preamp filter and removed cymbol resistor. At first it's more brittle as expected and a bit muddy. Will let that break in for a while before passing judgement.
Bias voltage using George's method is 25.3mv, 21.8, 28.9, 26.4 w B+ 353 vdc at 95vac. Too hot? Vintage fat bottles.

[vh junkie]

Yes, you should let the cap break in a dozen or so hours. I have never used one of these caps, I have been using the (2) 16uf TADs. The cymbal crash cap can be any thing up to 220k, only if you detect crash on top of the power chords. IMO 350 is too low, to me even 385 can be too low (depending on the amp). Some amps sound better well above 400. Do you have a PB, or something, to protect the speakers if necessary?

[YMI5150?]

is it low because of the metro PT? I think at full 120 VAC it only got to 460 or so. I had the variac at 90 for a while and a few people thought the amp sounded cold. bias voltage was fine but B+ was really low. I'll try 100 and see how she sounds.

I'm running a slave setup. I've got a Hot Plate set to line load and a line out box. the line out of the HP runs to a HotWire Lexicon reverb pedal and both lines go into a Peavey Classic 60/60. two cabs and its balanced to sound much like the first record. spoiled...

I'll break this cap in and dial in the sweet spot on B+, then record a clip for the record.

[vanhalen5150]

I have a hard time understanding the sound you guys mean with the symbal crash. Is it a sudden high end buzz?

[YMI5150?]

I heard a high end ring that seemed to not belong so I added it. I took it off the other day and it does not seem to need to be there. I think the noise I was hearing were the filters forming.

Last night I was messing around and that Erie is way different than the F&t. My resonance mod on my model a acted totally different. With the F&t I could roll it back and the pup would go from sizzle to single coil but highs would not change, just gain. With the Erie, there was a lot more high end sizzle and with that pot backed off I lost high end and gain. So apparently the Erie allows much more high end through. It was also making some noise breaking in so I swapped it back out mainly because I lost control of my resonance mod. I haven't given up it was just too dramatic of a difference. Vh junkie, it did what u said, lightening things up, severely. I know it will mellow out after a few hours. It was like a blanket was lifted from the amp. Changed the entire voicing, not necessarily in the vh direction but we'll see. Pretty amazing actually.

[vh junkie]

The cymbal crash sound is just like the name says: you hit a power chord, and it sounds like a crash cymbal was struck at the same time. If you don't here it, you don't need the resistor.

This cap think is kind of alarming! I always thought the caps just changed the feel (touch response?) of the amp... of course, I have largely been using F&Ts so it makes sense that they would all sound the same. But, different brands (ARS, Rifas, TADS), see to brighten a dull amp up quite a bit. SO I have been replacing the F&Ts in my preamp and PI locations.

[YMI5150?]

this is the second experience in the last two weeks where different brands of the same value/constructed part dramatically affect tone. I'm curious where on the board that stops or becomes less significant. screens/mains matter as much as the first few stages of the preamp circuit?

[Strat78]

You need more Pihers and Iskras. The 10k 2W and 1W are still readily available. True NOS 68k Iskras 1/2W can be found out there too. Anyway, there are lots of fun things to try for sure. Try .022 mustard for the V1B bypass cap, perhaps that will soften that weedy element going on. A .022 brown drop sounds pretty good for the PI input cap. The V2A cathode resistor should probably not be a CC. Raise the V1B plate resistor to 120k and see what happens. Also instead of the carbon film 8.2k 2W cap, use a AB CC 10k 2W in series with the carbon film 10k. Time to get some cooler looking biasing caps too. Sounds like you have plenty of gain though, all of the above add a gain, but with a little more warmth (thanks Ben). Here are two 22uf Rifas for the pre amp filter caps, like Robert said, the respective grounds go to ground one and two (Larry ground):