It is currently Mon Mar 16, 2020 5:25 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 129 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9  Next
Go to page Previous  1 ... 5, 6, 7, 8, 9  Next
Author Message
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 6:34 pm
Offline
Hobbyist
Hobbyist

Joined: Fri Jan 24, 2014 5:08 pm
Posts: 6
I know it's an older thread, but it's still the most comprehensive thread I have come across. so I thought I'd add my experience and information with the SuperSonic 22.

A/C Voltage - 120.4 90% of the time (small variation to 120.4-120.5 for a brief moment)
TP2 - 417 (in the first minute of power on)
TP43(D38) - 413 (in the first minute of power on)

After 20 minutes or so of letting the amp warm up, here's my readings.

TP2 - 413-415, mostly 413.
TP43 - 410-413 on Clean Channel, 407-408 on Burn
TP40 - 19.8 was my factory set number, and I've been playing the amp for 2 months
TP41 - 18.8

Based on the calculator I was shooting for 23.7mV. As a result, I ended up with the following configuration on the Clean channel:
TP2 - 413-415
TP43 - 410-413
TP40 - 23.1-23.9, mostly sat at 23.7, right on the money
TP41 - 22.3-22.5, mostly sat at 22.3

And on burn I had the following:
TP2 - 412-413
TP43 - 407-408
TP40 - 25.0-25.3, mostly sat at 25.3
TP41 - 23.4-23.5, mostly sat at 23.5

Couple observations:
1.) As you can see above, the clean & burn channels are not aligned. I don't think it's an issue, Just wanted to share that they do differ, I chose to set bias against the clean.
2.) There are cyclical power fluctuations, there's these odd power fluctuations you can audibly hear, it sounds like a very faint tick followed by a short fizz coming from the board (not speakers), they happen every 8 seconds or so and last for 1 second... they cause a tiny drop of about 0.3mV then spike to .4mV, then settle back down.. IT Seems after 20 minutes of warm-up the system stabilized... I don't know if this is a common things during the warm up.
3.) Gaps of as much as 1.9 mV on a matched pair seem big based on what I have read so I thing I am going to find some new power tubes that are better matched.
4.) Bias definitely effects hiss, if you bring bias down to 12mV, it cuts it substantially, up in 30's there's a strong hiss.
5.) I'll note my amp in quite when nothing plugged in, when you have a guitar plugged in there's a fair amount of hiss even with volume completely off, the hiss starts to builds as you pass 3 on clean, and really gets noticeable on burn when gains go over 5/5 with the volume at 3 or higher.
6.) if I understand the amp design, the hiss is all found in the pre-amp stage, because you can plug in a dead cable into just the fx return loop and the amp goes dead-quite even at 10 volume.
Overall I'm very happy with the amp, but this sucker is spitting at me when I'm playing at the house in a quiet room it's a bit annoying, anywhere else I play its not enough to notice. you'd think they could have easily address that or offer a clean-up & low power switch.

Based on above, I had a few questions:

1.) Is a gap of 2.0 mV rather large for what should be a premium pair of matched tubes?
2.) would I benefit from changing AT & AX tubes as far as noise removal?

Wanted to thank all of you on this thread for your information, pictures. I never would have attempted this on my own. I am comfortable with electronics but bias setting is totally foreign to me. after doing it, I look back that it was super-simple.


Last edited by Kring on Fri Jan 24, 2014 8:15 pm, edited 1 time in total.

Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 6:46 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Try pulling the input tube (first section 12AX7, V1) & see how much this drops the hiss. If it is significant --- look for a real quiet 12AX7 or 5751. A selected spiral wound heater-filament 12AX7A or 7025 may do the trick. Or a nice mil spec 5751, selected for quietness.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 7:43 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Kring wrote:
...
1.) Is a gap of 2.0 mV rather large for what should be a premium pair of matched tubes?
2.) would i benefit from changing AT & AX tubes as far as noise removal?...


1.) Less than 2 mV out of 23 is really not that bad, not even 10% difference. The closer the better, but less than 2 mV difference is acceptable.
2.) Answered by BMW2002Ti

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 9:21 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Kring wrote:
Based on the calculator I was shooting for 23.7mV. As a result, I ended up with the following configuration on the Clean channel:
TP2 - 413-415
TP43 - 410-413
TP40 - 23.1-23.9, mostly sat at 23.7, right on the money
TP41 - 22.3-22.5, mostly sat at 22.3

And on burn I had the following:
TP2 - 412-413
TP43 - 407-408
TP40 - 25.0-25.3, mostly sat at 25.3
TP41 - 23.4-23.5, mostly sat at 23.5



Interesting, but not really a significant difference.

The difference between the vintage and burn channel is that burn adds V2A into the signal path. The power draw of that half tube is probably what accounts for the slight drop in plate voltage due to the additional slight load on the power supply.

http://support.fender.com/schematics/gu ... ematic.pdf

Now considering that the plate voltages and cathode voltages drift over a small range (they will never read exactly one value in my experience), the best approach is to average the measured values (unless one is really far off from its mate, then you have a problem).

For the vintage channel, if you average the plate voltage (you only measured one tube, you should also have measured TP42), then average the cathode voltage range for each tube (and then average the two cathode numbers together), you get 9 watts plate dissipation at idle. For a 14 watt tube (which is what most modern 6V6GTAs are) this give you about 64% max plate dissipation at idle (which is the number that you are really looking for, not a specific cathode voltage).

Now, if you do the same thing with the measured values for the burn channel, guess what you get? 9 watts/64% max plate dissipation at idle (unless I screwed up my math, which I don't think I did).

Bottom line, worrying about the power tube bias at vintage and burn settings is unnecessary as the difference between the two is insignificant. Set the bias at whatever amp setting you normally use and the other will be just fine.

_________________
Bill

Image


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 9:31 pm
Offline
Hobbyist
Hobbyist

Joined: Fri Jan 24, 2014 5:08 pm
Posts: 6
BMW2002Ti wrote:
Try pulling the input tube (first section 12AX7, V1) & see how much this drops the hiss.


Thanks, I tried that, didn't change it at all. Does that mean that it's pointless to switch out than?

FYI - I noticed that it's actually a GT-ECC83-S tube in there (factory form Fender).


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 9:37 pm
Offline
Hobbyist
Hobbyist

Joined: Fri Jan 24, 2014 5:08 pm
Posts: 6
I thought I would share for reference the stock Fender tube configuration:

V1-12AX7, GT-ECC83-S, both halves used for both channels.
V2-12AX7, GT12AX7-C, A for burn channel, B for both channels.
V3-12AT7, GT-12AT7, both halves are reverb driver.
V4-12AX7, GT-12AX7-C, A for reverb recovery, B for both channels.
V5-12AT7, GT12AT7, both halves for pi.
V6 - 6v6, GT-6V6-S, White 7 Matched Premium tube, output tube
V7 - 6v6, GT-6V6-S, White 7 Matched Premium tube, output tube

Credits to shimmilou in another thread for the usage, I added the specific GT part numbers. http://forums.fender.com/viewtopic.php?f=13&t=61006


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 9:38 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Kring wrote:
BMW2002Ti wrote:
Try pulling the input tube (first section 12AX7, V1) & see how much this drops the hiss.


Thanks, I tried that, didn't change it at all. Does that mean that it's pointless to switch out than?

FYI - I noticed that it's actually a GT-ECC83-S tube in there (factory form Fender).


ECC83 is the European designation for a 12AX7.

_________________
Bill

Image


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 9:40 pm
Offline
Hobbyist
Hobbyist

Joined: Fri Jan 24, 2014 5:08 pm
Posts: 6
Quote:
you only measured one tube, you should also have measured TP42


Thanks for info Bluesky, I'll probably be cracking it again in a week or so, a friend is going to bring over some tubes and we'll swap them out and see if anything changes with the hiss and readjust bias. I'll check TP42 as well.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Fri Jan 24, 2014 10:22 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Kring wrote:
BMW2002Ti wrote:
Try pulling the input tube (first section 12AX7, V1) & see how much this drops the hiss.


Thanks, I tried that, didn't change it at all. Does that mean that it's pointless to switch out than?

FYI - I noticed that it's actually a GT-ECC83-S tube in there (factory form Fender).


All sockets & tube pins are clean and treated with contact cleaner? Correct. If you pulled V1 and the amp still had bad background hiss --- you need to rule-out a wiring layout problem or a PSU issue. Then, a ground point issue. Esp check for poor bolted or soldered grounding points.

Elminating hiss can by a vexing problem. A step-wise approach may keep you from going insane.

The GT-ECC83S = Slovakian made tube. From the now defunct Ei factory.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sat Jan 25, 2014 12:37 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
BMW2002Ti wrote:
...The GT-ECC83S = Slovakian made tube. From the now defunct Ei factory.


Are you sure that they aren't made in the JJ factory for GT? All other GT S-versions that I've seen are made by JJ. :?: I doubt if GT is using Ei tubes, or if they ever did, it would be great, but I doubt it. I have 4 original Ei 12AX7s (Yugoslavia?), and they are great tubes.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sat Jan 25, 2014 1:20 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Shimmy,

You are prolly correct about recent made tubes. I have a few GT labeled Ei E83CC, bought in the 1990's. I believe that they have the -S suffix. Gotta check.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sat Jan 25, 2014 8:11 am
Offline
Hobbyist
Hobbyist

Joined: Fri Jan 24, 2014 5:08 pm
Posts: 6
According to Groove Tubes - they are different parts, I know same 12AX7's, but they sell them as different models:

12AX7-C --- Great chiming tone with sweet, warm midrange excellent for Marshall® and Fender® amps. Smooth distortion characteristics and one of the highest-output preamp tubes in the GT 12AX7 line, with very consistent quality.

GT-ECC83-S --- Our highest-gain preamp tube, this tube has a huge amount of gain, with terrific output that makes it a great choice for driving modern, complex high-gain circuits. It has a relatively high quality variance (making Groove Tubes pre-testing procedures especially important in this case), with a tight, strong and relatively bright tone that can really liven up a weak or tired old vintage amp or a new amp with grade-quality tubes.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sat Jan 25, 2014 1:56 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Yes, the C versions are Chinese, the S versions are Slovakian (JJ factory), The R versions are Russian (some are Sovtek, some are EH). The origin info used to be on the GT site, but they have changed the site so much and dropped some of the specifics. It is usually easy to tell the tube types by looking at the parts inside.

For 12AX7 types:
The Chinese will have a metal tab on the side of the Plates. The Slovakian (JJ) will have flat, double posts holding the getter at the top. The R versions will have the tell-tale saucer shaped getters (Sovtek and EH slightly different shaped getters from each other), and sometimes will still have the Russian labels on the tube.

I like to collect/use GT tubes, particularly the unusual ones, such as Winged C that they used at one time. If GT really used Ei tubes, I would like to get some of those as well, but I haven't seen or heard of them until now. I am still looking for some GT 5751 at a decent price, they haven't made those for some time now.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sat Jan 25, 2014 5:25 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Mike,

In the early 1990's I bought a bunch of Ei made, silver plate 12AX7 that were rinsed and had GT logo. Those are all gone. What I have left are a couple of sleeves of Ei Elite 12AX7EG, that look identical. Except for either the Ei logo or some other branded logo.

My understanding is that GT bought a lots of tubes from various makes and rebranded them. And their sources changed depending on availability. Ei is closed now, so I presume everything on the market is now NOS?

Look like these:

http://i.ebayimg.com/00/s/MTYwMFgxMTk1/ ... -/$_57.JPG


Top
Profile
Post subject: Re: Super-Sonic 22 Bias Level
Posted: Sun Jan 26, 2014 2:29 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Yes, GT has used a variety of tube manufacturers, I am apparently not aware of all of them. Your pictures do look just like the Ei that I have, except for the Plate color. GT branded Ei would be cool, I'll have to look for some, thanks for the info. The modern S version GTs are JJ made. I am still not sure that the Ei factory closed, but at least stopped production of some tubes due to lack of materials according to what I have read, but it's hard to say exactly what is going on.

Image

Image

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 129 posts ]  Go to page Previous  1 ... 5, 6, 7, 8, 9  Next
Go to page Previous  1 ... 5, 6, 7, 8, 9  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: