Twin Reverb sounds bad

[Bullet175]

My silverface T/R is bumming me out. Sounds bad. Ive been playing it for about 15 years and until recently never really noticed until some other people heard it and pointed it out to me. I suppose I had just gotten used to it. But now that I am aware of it its really getting to me. Its very bright and tinny harsh sounding with no warmth or depth to it. No matter where I set my levels or guitar or pickups I switch to it still sounds bad.

Back story is I got it and first thing I did was have the tubes changed out and the tone caps were changed out about a year ago. Someone suggested that the tubes may need replacing but I dont know.

Any suggestions?

[alerich]

Your tubes are 15 years old? Start with new tubes and a bias check/set and go from there. That may be all it needs.

[Bullet175]

Yes the tubes are 15 years old. I got the amp 15 years ago and at the time it didnt play at all. I put it in the shop (now closed) and they put a new set of Sovtek tubes in and I have been with those ever since.

Should I change them all the pre amps and the powers?

[alerich]

The power tubes definitely. Fifteen years of regular play is beyond the useful working life of a set of Sovtek tubes, particularly what they were making fifteen years ago. If you can afford to change the preamp tubes it would probably improve the tone. Most folks don't change the preamp tubes with every power tube change but again we're talking fifteen years here. You could get by with not replacing the trem tube as long as it works properly - it's just an oscillator and doesn't carry any audio.

Start with just the power tubes and see how that improves your tone. That may be enough for your tastes.

[Colas LeGrippa]

and check the bias........all the Fender amps that come in here are biased too cold. When i got my own super reverb amp, it was biased under 1/2 of the tubes rating. Imagine the change once corrected, not the same amp. Why don't you replace the preamp tube at the same time, 100 bucks more but prob. worth it

Colas

[Bullet175]

OK thanks for the input everybody. I guess I will go ahead throw down the coin and order a whole new set of tubes. I read the section on fender amp tube biasing/checking and it all looks pretty complex but Im sure its not as bad as it sounds. Ive had the chassis out of the cabinet many time so I am very familiar with whats in there. I will put the new tubes in and give it a go but will probably be back here with my numbers after checking it and see what you guys in the know think. Thanks again for your help. Trey

[floyd]

Better find out if your Twin has a true bias , or a bias balance set- up, before you proceed.

[Ed_Chambley]

What year and circuit is it?

[firemedic]

first thing I did was have the tubes changed out and the tone caps were changed out about a year ago.

How about the filter caps? Or is that what you meant?

[Bullet175]

Firemedic, yes the filter caps,
 
Ed where do I find this info. The only info I can find  is the tube placement sticker inside the cabinet.
 
What I can tell you is that I have no resistors from pin 8 to chassis. just a short piece of wire from pin 8 to chassis. A large pot is mounted to the chassis right behind and between the reverb and speed pots. Is that the bias tweeker? Is this an adjustable bias setup?

FYI I put the new tubes in.  Thats all,  didnt check bias "yet".  Left it a low volume and strummed a chord and instantly heard a big improvement over what I had before. The chassis is out of the cab right now. can someone give me a basic rundown on how to test the bias on the amp. Or do I need more info on the amp?

[Bullet175]

Edit to above post.  I just did a quick voltage check of the power tubes using the Hoffman biasing instructions. Tested from pin 5. Results are
from left to right facing rear of amp.

tube 1 = 470 volt
       2 = 470 volt
       3 = 470 volt
       4 = 470 volt

Is that good or bad?

[sluckey]

I think that's not pin 5. Pin 5 should be approx. -50 volts.

[Ed_Chambley]

Ed where do I find this info. The only info I can find  is the tube placement sticker inside the cabinet.
 

[/quote]
The serial number on the chassis should give you the year providing it is original.  From there you can go to ampwares.com, find the schematic for that year.  This will let you know if you have a balance pot or a bias adjustment, or you could take some photos of the chassis inside and post them.  Make sure you get good shots of the bias section and adjustment pot.  If you have a bias balance and not a bias adjustment you may want to consider converting it to a bias adjustment.  I don't want to get the cart before the horse, but I think you would prefer an easy way to adjust bias.  I have a Twin and if it runs cold it is nothing but loud and thin.

The tube chart usually has the circuit identified on it, but they are not always correct.

[Bullet175]

Sluckey I did read a pin on each tube that did read exactly -50.  Its so hard to see the numbers on top of the tube sockets with all the wires and whatnot in the way.

Chassis serial number is B 01056. But from what I was reading nothing about that number looks right. If 56 is supposed to indicate the year then it cant be right. I will try to get some pics up soon.

EDIT  OK I found it. Its a 1975. Found this PDF for the drawing. This looks like the inside of mine.  http://ampwares.com/schematics/100W_Mast_Vol_SF_Twin_Rev.pdf 

[g-man]

Deleted

[Ed_Chambley]

Sluckey I did read a pin on each tube that did read exactly -50.  Its so hard to see the numbers on top of the tube sockets with all the wires and whatnot in the way.

Chassis serial number is B 01056. But from what I was reading nothing about that number looks right. If 56 is supposed to indicate the year then it cant be right. I will try to get some pics up soon.

That number indicates 75 or 76.  I attached a schematic and which could be it.  Check the layout page and see if it matches yours.  If so, it will have bias balance.

If you have trouble counting the pins, look at the key from the inside and count clockwise.  Pin 1 is the first one to the left of the key and 8 is the last one which is the first one to the right.  If what you have is a AA270 (see if the tube sheet has it on it) it is a great amp to Blackface as it is called.
If it has a master volume, it is likely to be the second attachment.  Doug has instructions in the library Here
http://www.el34world.com/charts/bias_conversions.htm
which explains bias circuits.  Very useful information to help understand the differences and how to change yours if you want to do so.  There could be a number of reasons it is sounding thin, but I have converted a 75 twin recently and changed it to an AB763 circuit with new caps and it really sounded nice, although I have played the others that were not modified and they sounded good as well.  It is a matter of preference, but more people prefer the Blackface tone most.  Insuring your tubes are working properly and then go from there.

[Bullet175]

OK Ed, I looked at that and mine is the second schematic. Master volume amp. And the schematic shows 470 volts off pin 4. And thats what Ive got. I went and re tested now that I know my pins #s.

The only number I can find other than fenders zip code on the tube chart is the number 047944 on the lower right corner.

My question is on the conversion. Is this an upgrade to a newer blackface layout? What exactly would I be achieving by doing a conversion?  It seems like a pretty simple thing to do. Just moving some stuff around right?

[sluckey]

I highly recommend fixing the amp as is before even thinking about modifying it. Otherwise, you have no baseline to compare to see if the mods improved anything.

[Ed_Chambley]

I highly recommend fixing the amp as is before even thinking about modifying it. Otherwise, you have no baseline to compare to see if the mods improved anything.

+1, I will bow out.  Follow Sluckey's lead.  You may really like the amp once you get it back to good operation.  The conversion is not difficult to answer your question, but you still have (or it seems) problems to work out first.  With the age of the amp I would consider new tubes and caps unless it has been recapped recently.  I am not clear on the current condition, but if everything is working correctly they sound good, just different.  It has a little more power and most people do not like the master but I find it very usable on this amp.  Once you have a good matched set you can get your amp bias correct.  Might be all you need, but if not you can always continue.

[Bullet175]

Oh I have no intentions of modifying the amp at this time. I was asking just out of curiosity since it was brought up what is the conversion all about. I thought we were moving towards me getting my amp biased. I have already replaced the power tubes, filter caps  and the preamp tubes two days ago. The amp now sounds a whole lot better than it did. Its fuller and it does not flabby out my speakers anymore. But I have not put it through its paces yet because I was told in an above reply to be sure to bias the amp after I installed the new tubes. What I would like to know is in a nutshell is, what is biasing and how do I determine if the amp is biased correctly.

[Willabe]

 

http://www.el34world.com/charts/fenderservice5.htm

http://www.el34world.com/charts/Biascircuits.htm



               Brad