PAB: For clean, OD, or both?

[crholguin]

Hello, Garage mates,

I'm a friend Gil's, Chris's, and Bill's, but am new to this forum. With Gil's encouragement and invaluable help (and a chassis, trannies and boards from Brandon), I just finished my first build from the ground up (non-HRM Skyliner).

I think the clean on this amp is just about perfect: chimey, but sans ice-pick-in-the-ear highs regardless of pickups.

I do have a question about how the experienced here use the PAB and OD.

Option 1: OD trimmer > ~15k to ground. Here, I find I cannot kick in the PAB without low-end fartiness, although the highs are nice and smooth. I tried various tubes in the OD socket, and that did make a substantial difference. But even with the best of them the fartiness makes the neck pup on a Strat all but useless, and even the bridge has a bit much flatulence for my taste. The fartiness does diminish as the amp gets louder, but is pretty unacceptable at bedroom levels.

Without the PAB, I tend to like the OD trimmer at ~40k to ground so there's pretty much equal gain to both OD triodes.

I read somewhere here that the OD is designed to be used with the PAB, which if true would argue for setting the OD trimmer pretty low.

Option 2: OD trimmer ~15k to ground. I can kick in the PAB with the OD without fartiness, but the OD tone alone is pretty anemic.

Scenario 3: Mid switch instead of PAB. Unlike the PAB, kicking in the mid switch doesn't seem to impart much flatulence with the OD trimmer set pretty high. Trouble is, the clean is just about perfect without the mid switch on, and running back and forth to the amp to flip a switch doesn't sound very viable. I suppose I could put the switch on a relay.

Another solution would be to install a switched Smooth & Slim-type filter that would kick in only when both PAB and OD are on. Not sure I have the electro-chops to pull that off, though it does seem to me that would a real fix.

My basic questions, to those who would be so kind as to offer the benefit of your experience, are these: Is the above pretty much normal with this circuit or do I need to trouble-shoot the OD on my build?

If it is par for the course, do most favor using the PAB with the OD or just to boost the clean in a band setting?

BTW: Pix of the build are here:

http://picasaweb.google.com/crholguin/M ... directlink

TIA and Happy Holidays,

Carlos.

[Normster]

Hard to tell by the pictures, but it looks like you have the OD coupling caps reversed (judging by cap size). OD1 coupler should be .01uF and OD2 should be .005uF. If they are indeed switched, it could be contributing to the farty bass.

BTW, welcome to the forum!!!

[brownnote]

welcome!

What power transformer are you using?

Just going by common color conventions, it looks like you have your 6v & 5v windings crossed, with the 6v winding going to the relays and your 5v winding to the heaters.
If that is the case, and your heaters are underpowered, that would explain some...

[heisthl]

I just finished my first build from the ground up (non-HRM Skyliner).

Welcome to the Forum - nothing make you feel better than a successful build.

I do have a question about how the experienced here use the PAB and OD.
I read somewhere here that the OD is designed to be used with the PAB, which if true would argue for setting the OD trimmer pretty low.

Not on the non-HRM, it's the HRM amps that need PAB with the OD.

Scenario 3: Mid switch instead of PAB. Unlike the PAB, kicking in the mid switch doesn't seem to impart much flatulence with the OD trimmer set pretty high. Trouble is, the clean is just about perfect without the mid switch on, and running back and forth to the amp to flip a switch doesn't sound very viable. I suppose I could put the switch on a relay.

The footswitchable Mid Boost is the best feature you can add to a non-HRM, almost essential and very useful

If it is par for the course, do most favor using the PAB with the OD or just to boost the clean in a band setting?
Carlos.

Bingo - IMHO you really have 2 choices, use it like a clean boost or redo it as the Mega Boost (lift the mid and bass pots 470k off ground) so you can use it as Marshall on 10 simulator.

[glasman]

welcome!

What power transformer are you using?

Just going by common color conventions, it looks like you have your 6v & 5v windings crossed, with the 6v winding going to the relays and your 5v winding to the heaters.
If that is the case, and your heaters are underpowered, that would explain some...

Yup I agee. 5V are yellow. 6.3 are green

[crholguin]

Hard to tell by the pictures, but it looks like you have the OD coupling caps reversed (judging by cap size). OD1 coupler should be .01uF and OD2 should be .005uF. If they are indeed switched, it could be contributing to the farty bass.

BTW, welcome to the forum!!!

Pretty sure they're right: the smaller cap is a "103" and the larger a "472." Both are 630v, but the larger cap is the only one of the Xicons on the preamp board that isn't an "F" series, so that may explain the paradoxical size differential. I suppose it could also be mislabeled, though that seems a long shot. I do have an F series .0047uF/400v I could try.

Thanks much for the reply and the welcome.

Carlos.

[glasman]

Hard to tell by the pictures, but it looks like you have the OD coupling caps reversed (judging by cap size). OD1 coupler should be .01uF and OD2 should be .005uF. If they are indeed switched, it could be contributing to the farty bass.

BTW, welcome to the forum!!!

Pretty sure they're right: the smaller cap is a "103" and the larger a "472." Both are 630v, but the larger cap is the only one of the Xicons on the preamp board that isn't an "F" series, so that may explain the paradoxical size differential. I suppose it could also be mislabeled, though that seems a long shot. I do have an F series .0047uF/400v I could try.

Thanks much for the reply and the welcome.

Carlos.

Hi Carlos, You are correct. I just pulled them from my parts bin and the .01 is smaller than the .0047uf. One is metallized (.01) and the .0047uf is non-metallized.

Gary

[crholguin]

welcome!

What power transformer are you using?

Just going by common color conventions, it looks like you have your 6v & 5v windings crossed, with the 6v winding going to the relays and your 5v winding to the heaters.
If that is the case, and your heaters are underpowered, that would explain some...

I believe it's a Heyboer. My understanding is that it has a 6.3v ac tap for the relays. I'm pretty sure it's the same one Gil used in his No. 9 amp, and I wired it up the same way.

The in-circuit voltages are a bit jumpy, but my meter reads 7v ac across the green leads, and 6.9v ac across the yellow.

Does this seem wrong?

Thanks for the reply and the welcome.

Carlos.

[brownnote]

I believe it's a Heyboer. My understanding is that it has a 6.3v ac tap for the relays. I'm pretty sure it's the same one Gil used in his No. 9 amp, and I wired it up the same way.

The in-circuit voltages are a bit jumpy, but my meter reads 7v ac across the green leads, and 6.9v ac across the yellow.

Does this seem wrong?

Thanks for the reply and the welcome.

Carlos.

Hi Carlos,
interesting....
It does look like you have them reversed, but the voltages are high, so in this case it might not be a bad thing.
Heater voltages above 7v can cause some undesirable tonal effects as well.
What are your other voltages (preamp, PI, power tube plates, etc. ?
Does the PT have multiple primary taps? ...never mind I just looked, it doesn't.
What is the AC line voltage in your home?

[crholguin]

I just finished my first build from the ground up (non-HRM Skyliner).

Welcome to the Forum - nothing make you feel better than a successful build.

I do have a question about how the experienced here use the PAB and OD.
I read somewhere here that the OD is designed to be used with the PAB, which if true would argue for setting the OD trimmer pretty low.

Not on the non-HRM, it's the HRM amps that need PAB with the OD.

Scenario 3: Mid switch instead of PAB. Unlike the PAB, kicking in the mid switch doesn't seem to impart much flatulence with the OD trimmer set pretty high. Trouble is, the clean is just about perfect without the mid switch on, and running back and forth to the amp to flip a switch doesn't sound very viable. I suppose I could put the switch on a relay.

The footswitchable Mid Boost is the best feature you can add to a non-HRM, almost essential and very useful

If it is par for the course, do most favor using the PAB with the OD or just to boost the clean in a band setting?
Carlos.

Bingo - IMHO you really have 2 choices, use it like a clean boost or redo it as the Mega Boost (lift the mid and bass pots 470k off ground) so you can use it as Marshall on 10 simulator.

Thanks. I suppose every amp has its idiosyncrasies, but since this is my first build of an amp I have no experience with, I figured I better rule out build problems before settling down to happy coexistence.

I still need to build a cabinet for the project. (I tried taking it out to play as is, but it's just too heavy and festooned with expensive glass to attempt that again.) After that, I think I'll make the mid boost switchable.

Best,

Carlos.

[crholguin]

I believe it's a Heyboer. My understanding is that it has a 6.3v ac tap for the relays. I'm pretty sure it's the same one Gil used in his No. 9 amp, and I wired it up the same way.

The in-circuit voltages are a bit jumpy, but my meter reads 7v ac across the green leads, and 6.9v ac across the yellow.

Does this seem wrong?

Thanks for the reply and the welcome.

Carlos.

Hi Carlos,
interesting....
It does look like you have them reversed, but the voltages are high, so in this case it might not be a bad thing.
Heater voltages above 7v can cause some undesirable tonal effects as well.
What are your other voltages (preamp, PI, power tube plates, etc. ?
Does the PT have multiple primary taps? ...never mind I just looked, it doesn't.
What is the AC line voltage in your home?

VDC at preamp/splitter plates:
V1: 181/175
V2: 179/180
V3: 284/273

Output plates and screens measure 444v.

House voltage is 121.5vac

Thanks,

Carlos.

[tubedogsmith]

I think Brandon has his PT's wound with two 6.3v windings. I've noticed and amp or two of Gil's wired the same way I think.

[crholguin]

I think Brandon has his PT's wound with two 6.3v windings. I've noticed and amp or two of Gil's wired the same way I think.

Yes. Also, the yellow leads are something like 16awg, whereas the green leads are maybe 20awg. Since both secondaries put out the same voltage, wouldn't it make sense to go with the beefier wire to the heaters? I would think the relays' current draw would be relatively light.

It sure would have been easier to pop those big yellow leads into eyelets on the relay PS though. Fitting them into the socket terminals along with the anti-hum resistors and jumpers to the next set of heaters was a bit of a PITA.

Carlos.

[Funkalicousgroove]

Yes, that is correct, Yellow is 6.3@10A and green is 6.3@ 1A.