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Retubing Fender Showman

8/14/1997 9:52 AM
Bob	Retubing Fender Showman I would like to retube my '93 Fender Dual Showman. The store I buy my gear from was out of matched "Quad" sets, but he said that I could take two matched "pairs" and it would have no effect on tube life or tone. My question is: 1) Is the sales man correct? (I never really trust salesmen), and if he is correct what is the correct positioning of the new tubes in this amp. Biasing on this amp is no problem for a non techno-type like myself, it has convienient ports on the back and all I need is a DMM and a screwdriver. Thanks....BC

8/14/1997 9:52 AM

Bob

Retubing Fender Showman

I would like to retube my '93 Fender Dual Showman. The store I buy my gear from was out of matched "Quad" sets, but he said that I could take two matched "pairs" and it would have no effect on tube life or tone. My question is: 1) Is the sales man correct? (I never really trust salesmen), and if he is correct what is the correct positioning of the new tubes in this amp. Biasing on this amp is no problem for a non techno-type like myself, it has convienient ports on the back and all I need is a DMM and a screwdriver.
Thanks....BC

8/14/1997 1:00 PM
J Fletcher	Assuming you can adjust the overall bias with one back panel trimmer and the balance between the two sides with the other trimmer,put one matched pair(A) in the 1st 2 sockets and the other matched pair(B) beside the 1st pair(ie.AA BB)Then follow the bias adjust instructions.Unless the two pairs are way out of whack with each other,this should work fine.I'd be more concerned with who makes these tubes,and what type they are,than buying them matched.Are they Fender tubes?

8/14/1997 1:00 PM

J Fletcher

Assuming you can adjust the overall bias with one back panel trimmer and the balance between the two sides with the other trimmer,put one matched pair(A) in the 1st 2 sockets and the other matched pair(B) beside the 1st pair(ie.AA BB)Then follow the bias adjust instructions.Unless the two pairs are way out of whack with each other,this should work fine.I'd be more concerned with who makes these tubes,and what type they are,than buying them matched.Are they Fender tubes?

8/14/1997 1:01 PM
R.G.	He's right - kind of. You can use two matched pairs, with only a little subtlety. You want to put ONE of each matched pair on each electrical side of the output transformer. This keeps the output transformer balanced even if the two pairs are not matched; you have one of each pair on each side. The subtlety is this: If the pairs aren't matched to each other, then one pair will pull more current at idle than the other, by definition. If this imbalance is too bad, you will have an exposure to some problems that may be trivial or nonproblems, or may be ugly, depending on the amount of mismatch. If they are fairly close, then he's right, you won't even hear it. You can get all points in between depending on how close they are. It used to be that tubes were close enough that this was not a big deal, but the variation in characteristics of new-manufacture imports is such that you can now get some big imbalances. You COULD have: - crossover distortion that you can't easily get rid of by biasing because one pair may be cut off or nearly cut off while the other pair is pulling too much current and is already well into class A for small signals - imbalances get worse because one pair is not working as hard, so the other pair is overheating; the overheated pair age faster

8/14/1997 1:01 PM

R.G.

He's right - kind of. You can use two matched pairs, with only a little subtlety. You want to put ONE of each matched pair on each electrical side of the output transformer. This keeps the output transformer balanced even if the two pairs are not matched; you have one of each pair on each side.

The subtlety is this: If the pairs aren't matched to each other, then one pair will pull more current at idle than the other, by definition. If this imbalance is too bad, you will have an exposure to some problems that may be trivial or nonproblems, or may be ugly, depending on the amount of mismatch. If they are fairly close, then he's right, you won't even hear it. You can get all points in between depending on how close they are. It used to be that tubes were close enough that this was not a big deal, but the variation in characteristics of new-manufacture imports is such that you can now get some big imbalances.

You COULD have:
- crossover distortion that you can't easily get rid of by biasing because one pair may be cut off or nearly cut off while the other pair is pulling too much current and is already well into class A for small signals

- imbalances get worse because one pair is not working as hard, so the other pair is overheating; the overheated pair age faster

8/15/1997 5:07 AM
Bob	Thanks for the info.....I think that my best bet is to mail order A matched Quad set (and new preamp tubes also) from Hoffman's. I was planning on buying Sovtek 5881s and 121ax7wa's, I already have some new 12at7s. My main reason for chosing Sovtek tubes in this case is money. This thing has 11 tubes, and I would like to keep the cost of retubing this amp below $100. The tubes that are in the amp now are the stock Fender tubes. I dont't know who makes their peramp tubes, but the power tubes have "Made in China" stamped below the Fender stamp. Currently, it sounds OK, I just think that it can sound better. My main goal for this amp is to get a huge clean tone that has a "sweet" disposition. I just bought this amp and it seems like a good choice for what I'm after. Are there any other tubes manufactures or types that you folks might recommend......I've done the NOS tube thing im my '67 Super and have had mixed rusults. As a result, I am leary about going that route.

8/15/1997 5:07 AM

Bob

Thanks for the info.....I think that my best bet is to mail order A matched Quad set (and new preamp tubes also) from Hoffman's. I was planning on buying Sovtek 5881s and 121ax7wa's, I already have some new 12at7s. My main reason for chosing Sovtek tubes in this case is money. This thing has 11 tubes, and I would like to keep the cost of retubing this amp below $100. The tubes that are in the amp now are the stock Fender tubes. I dont't know who makes their peramp tubes, but the power tubes have "Made in China" stamped below the Fender stamp. Currently, it sounds OK, I just think that it can sound better. My main goal for this amp is to get a huge clean tone that has a "sweet" disposition. I just bought this amp and it seems like a good choice for what I'm after.

Are there any other tubes manufactures or types that you folks might recommend......I've done the NOS tube thing im my '67 Super and have had mixed rusults. As a result, I am leary about going that route.

8/15/1997 7:15 AM
John Martin	Yes, hold out for the matched quad. No reason to do otherwise. The newer straight bottle Chinese tubes are ok, stay away from the "coke bottle" shaped ones. The Sovteks seem to have that "sweeter" sound as compared to the Chinese tubes. Also good are the Svetlana 6L6s if you can get them. Tesla now has some 6L6s out but I have not heard them. I have been very pleased with Tesla's other power tubes, I might add. Some of the Chinese preamp tubes seem to have a little more "agressive" sound, but the Sovteks are very consistant. I buy these 100 at a time so I have a reasonable sample base. If you decide on the Sovtek 5881s, get the WXT version, They have the full base that fits the tube grabbers on Fenders. The wholesale price between the two is less than a dolla, so don't let anybody rip you off. JM

8/15/1997 7:15 AM

John Martin

Yes, hold out for the matched quad. No reason to do otherwise.

The newer straight bottle Chinese tubes are ok, stay away from the "coke bottle" shaped ones. The Sovteks seem to have that "sweeter" sound as compared to the Chinese tubes. Also good are the Svetlana 6L6s if you can get them. Tesla now has some 6L6s out but I have not heard them. I have been very pleased with Tesla's other power tubes, I might add.

Some of the Chinese preamp tubes seem to have a little more "agressive" sound, but the Sovteks are very consistant. I buy these 100 at a time so I have a reasonable sample base.

If you decide on the Sovtek 5881s, get the WXT version, They have the full base that fits the tube grabbers on Fenders. The wholesale price between the two is less than a dolla, so don't let anybody rip you off.

JM

8/15/1997 10:44 PM
Heath	I just put a set of Sovtek 12AX7WXT+'s in an amp I was working on and I think they're great, Sovtek also seems to think they're great as well as they've run a full page advertisement in Glass Audio's "World Tube Directory" or whatever it's called for these tubes.

8/20/1997 4:35 AM
Bob	While looking at some new power tube boxes, I noticed that the Sovteks and Sventlanas have a green sitcker with a handwritten number (320, 275, etc.). I also noticed that in the matched sets these numbers were all the same. Is this the notation for the "grade" of the the tube made during the testing/sorting process? If so, are the lower numbers "softer" tubes, and higher numbers "harder"tubes? These are the things that keep me awake at night wondering about BC

8/20/1997 4:35 AM

Bob

While looking at some new power tube boxes, I noticed that the Sovteks and Sventlanas have a green sitcker with a handwritten number (320, 275, etc.). I also noticed that in the matched sets these numbers were all the same. Is this the notation for the "grade" of the the tube made during the testing/sorting process? If so, are the lower numbers "softer" tubes, and higher numbers "harder"tubes?
These are the things that keep me awake at night wondering about

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