V4 PCB component repair/updating

[Liquids]

Steve - are we talking D5 or Faderlube? Faderlube is meant to be a lubricant, D5 is meant to simply be an cleaner for electronics and switches (etc), but both (and other) products are under the Caig-->Deoxit line, though very different in function.

[Hangman]

Steve - are we talking D5 or Faderlube? Faderlube is meant to be a lubricant, D5 is meant to simply be an cleaner for electronics and switches (etc), but both (and other) products are under the Caig-->Deoxit line, though very different in function.

yes, I am talking about D5. it leaves behind an oily residue.

faderlube would be worse by far, but D5 leaves behind some sort of oily "protectant" I've found that it just builds up, and builds up. getting a cleaner that doesn't leave a residue makes a big difference.

[beedoola]

What is the MA reading I should want for the tubes? I measured them and got around 19.5-20 MA

I replaced R49 with the stock value when I worked on the amp. R50 was already replaced prior to my obtaining the amp.

[Hangman]

19.5-20ma is on the low side of things, but as Liquids mentioned, that doesn't necessarily mean anything in regards to the V4.
These amps run the tubes hard, and running the bias cool isn't a bad idea. typically I tend to see tubes bias up anywhere from 19-26ma in a stock V4. so you're in that range.
you could increase it a little if you want... might be an interesting experiment for you.

[Liquids]

So all four tubes are biasing up in that zone?

FYI One needs to know the tube and the plate voltage to get an idea of where your idle bias is, even with the idle current/bias spec(s) figured out.

We know the amp, the tubes, and we know your voltages from what you've posted...

So, following, here's some of the info given by that bias calc I linked to before, with the voltage range you are getting on the plates.

Results: For 535 Volts
6L6GC (Max disapation 30 watts)
60% - 34ma
70% - 39ma
80% - 45ma
100% - 56ma

So 20ma of 56ma (20/56) is 36% max bias at idle.
26ma would be 46% max bias at idle.
50% of max bias at idle would be 28ma. I personally wouldn't go over that with most tubes.

[Now, some say the 7027s are 35w tubes. If someone is using NOS tubes, ok, go ahead and change the calc...I say, unless they're NOS, treat/bias them as what they probably are - 30w 6L6GCs at HV (~540v depending on the ampeg...)]
I bias for 1) tone and 2) longevity

Yes, in almost any other amp, this 36% bias zone would be cold. How's it sound to you?

I had a bias trim pot in there and dialed in everything from cut off (super low at idle) to 70%, at both low and turned up volume, and listened. I've done the same with Fenders. In the ampeg, I thought the cooler bias happened to sound best--cooler bias like you have offered HUGE lows, and no mid-range mush. Big, loud, clean, but not harsh. I put back the stock value resistor, and have left it ever since. Note: with blackface style fenders and 6L6GCs, , I tend to like the bias closer to 50- 70% to get more mids I suppose.

To me, the key is if one tube is drawing notably different current than the others. I think your bias is fine. This was just in response to your seeing glow on transients in some tubes more than others. If they all bias in the same zone, you're OK, it's just the tubes.

I'd suggest, leave it like this, and see how the tubes do over the course of a month or so, if anything develops. If all goes well, and you want to mess with the bias, THEN if you want to consider adjusting the bias, it makes more sense--AFTER you know the amp is good and stable at a decent bias point...in fact one or more tubes may drift in how they are biasing with some use, even in a month, at these voltages. You'll know more later.

I think the key info here and now:
1) It sounds OK, stable and it's holding up well after all the work you did on it?

2) Since we know where it's biasing at generally, is there much difference in bias from tube to tube?

[beedoola]

Sounds good, plenty of low end. I'm just wondering if that 20MA is too low.

I checked each tube, in the same socket, just changing the bias probe from socket to socket, and got anywhere from 19.5-20.5. Most of them were in the mid to high 19MA.

[Liquids]

The only "too low" is if the tubes are in cutoff, crossover, or just plain sounds bad. TDon't loose sleep over it. The amp wasn't designed with adustable bias, and ran old school 7027s this cool, by design, not by accident. Enjoy the amazing amps tones and the extended tube life!

[syscokid]

In the ampeg, I thought the cooler bias happened to sound best--cooler bias like you have offered HUGE lows, and no mid-range mush. Big, loud, clean, but not harsh. I put back the stock value resistor, and have left it ever since. Note: with blackface style fenders and 6L6GCs, , I tend to like the bias closer to 50- 70% to get more mids I suppose.

I personally agree with this, too. I have a set of JJ 7027A's. These are definitely 30 watt tubes...unlike the original American made 7027A's which were actually 35 watt tubes. With a 528vdc at the plates, the bias on my VT-22 is set at 34ma's. It's a "cool" setting that to me it's win-win situation because the amp sounds right to me, and promotes longevity for the tubes.
BTW, here's my Adjustable Bias Mod:




I should have plenty of range with this setup - should I go insane and invest in a set of some NOS 7027A's...if they even exist! Oh yeah...there's not much of a margin for a shaky screwdriver, so I always use a insulated one!

[Liquids]

With a 528vdc at the plates, the bias on my VT-22 is set at 34ma's. It's a "cool" setting that to me it's win-win situation because the amp sounds right to me, and promotes longevity for the tubes.

Hey, set it where you like it!

34ma is ~60% bias at idle though... Still, if someone else says they prefer the bias set at 75% and their tubes weren't croaking, hey, use what you like. I am just against people not audio testing and going with the "I read it on the internet/the tech told me" that the hotter the bias the better kind of thing. I was surprised I like it biased cold, but my ears hear what they hear, and its about the tone I'm after, and some people might be after something completely different...

I should note...I've messed with the EQ a fair bit, circuit-wise. And BTW I don't cut or boost any mids via the mid pot, unless I want to simulate certain sounds for kicks...though there is the obvious scoop from boosting the bass pot and the treble pot the way I have it set, etc, so it's certainly not a cold bias with a flat EQ setting.

And tubes are replaceable, after all...well, at least at this point in time.

I'm a bit sad and it also is a bit rattling that the Winged C factory closed. Hoping it's temporary (like a shift to producing tubes or something else for the Russian gov't but eventually back to tube for market)?

Don't be afraid to use some of the Sino tubes AES and others offer in this amp...I've found them solid in the cost/tone ratio stuff. Of course, at higher bias, maybe the JJs or better yet, the New Tung Sols(?) would be more robust among what is available...

[beedoola]

I had a question regarding the Hum Balance pot and general ground noise.

When I turn my V4 On from Standby, I get some noise/humming. This slightly quiets when the volume control on the amp is turned up slightly from being full Off.

I tried the hum balance control but got lots of noise throughout the sweep of the control until each end of the HB control: fully counter clockwise and the lots of noise stops, and the noise level is back to its initial humming. Turn the HB control fully CW and the same thing, but in-between on the control is noise.

I added a three prong cord, and removed the death cap. The polarity switch is still hooked up, and that doesn't seem to have any effect on the noise/hum I'm experiencing.

The hum level seems to be both at home and my studio, though perhaps more at the latter, or perhaps it is perceived as more because I'm running the amp through a 4x12 vs a small speaker at home for testing purposes.


EDIT**** I noticed today that there was a fair amount of hum, like I was talking about, but it was only on Input 1, and only when the Sensitivity rocker was at its lowest - to the left, if viewing the control panel. When the sensitivity is in the middle position, it also produces the hum, but not when all the way up/to the right.

Input 2 and Volume 2 do not have this issue - the Sens. rocker can be in any position and I don't get that hum.

Any thoughts?