Do you really need to replace all tubes on a tube amp at the same time?

[TalismanRich]

FWIW, if the rectifier tube that is in there is any good, then I see no reason to worry, or even replace it.. Rectifier tubes simply convert the AC to DC. They don't even process the audio at all. Any changes in the "sound" would be due to the ability of the tube to maintain sufficient and constant voltage for the other tubes, especially under high demand.

I've only changed 1 rectifier tube in the past 10 or more years. I've changed several sets of power tubes and several preamp tubes over the years. Power tubes were done in matched pairs or quads as appropriate. Preamp tubes were replaced as needed, usually for becoming microphonic in combo amps. Tap on the tube, if it goes ZINGGG, pull it and put in a new one. Those little grid wires can bang around when you're cranking through a speaker 6 inches away. They get noisy.

50 years ago, we just went down to Radio Shack or Walgreens, bought a couple of tubes for $3 a pop "just in case" and off we went. Our bassist once blew out his set of 6550s in his Traynor amp during a dance. At break, he ran down to the drug store a couple blocks away, bought 4 tubes, came back and threw them in. (yeah, they sold tubes in drug stores... even had tube testers in a lot of them) We didn't bother with matching or biasing or anything. Plug them in and go!

 

[ecc83]

Ah! THEM'S wuz the days Rich! Sadly today's GZs are not what they were 40 years ago and some brands are prone to flash over. This problem is greatly worsened by that devilish invention the Stand By Switch!
You only ever find them on valve guitar amplifiers and why people want them I have never figured out!

Save power? Who cared a **** until a couple of years ago and in any case if you really wanted to save juice, turn the bloody lot off! The poor valve gets hit with AC when the OP stage is heated and the caps discharged and so has to supply a huge whooomp of current.

There were some fairly reliable GZ34s but 'we' could not be sure peeps would fit them so we had to mod the rectifier circuit to minimize the shock of the SBSwitch. Could not you see market a top end 30W amp without one.

BTW I do agree that the rect will not affect the sound one iota.

Dave.

 

[RFR]

What I wonder is where those tube testers that were everywhere all went to.

 

[ecc83]

What I wonder is where those tube testers that were everywhere all went to.

When I was a 'prentice R&TV eng' it was my job to test valves that customers would bring into the shop. Mullard tester it was and used Paxolin cards about 1mm thick with a pattern of holes punched out on them. You inserted the appropriate card for the valve in the back of the machine and plugged a valve in the right base. Pulled a big chrome handle and the valves condition came up as green fluorescent line from a discharge tube.

I can still remember we charged 6d (2.5 new p) per valve but waived the fee if they bought a new one!

People would come in with a carrier bag with up to a dozen valves out of a telly. We were quite sure they had no 'king clue how to put them back in the right place when they got home! This would have been early 1960s.

Dave.

 

[gene12586]

One cannot be 100% sure about anything in life, least of all valves! They could fail at first blast (V unlikely) or last 20 years. OK, enough platitudes! Bear in mind that new valves only have a 90 day warranty and so I would get them in the amp ASAP and give it a good shake down. Listen especially for any crackles and pops. These will most likely come from the first valve in the circuit. Where you have two OP valves they should be matched* and give a low hum level. Note the level with all controls at zero then check it with the new ones. If the hum is louder, complain.

How much hassle is it to get the chassis out and change the valves? If muchly so I would wait for the rectifier. Note, so long as you are sensible where you put your fingers you can run the amp out of its cab, could be handy. Cannot recall if the amp needs the bias set? Once you have thrashed it for an hour or two, leave it off for the HT caps to drain. Overnight if no tiny fingers can get at it.

*you can of course buy "matched" pairs and quartets but in my experience two stock EL84s or whatever 'off the shelf' are close enough. Keep to the same brand mind. I did some tests some years ago and found so called matched sets were no better than a random selection... other's MMV.

Dave.

Thanks. I know all the positions the specific preamp tubes need to be in.
I'll probably just end up playing my practice amp till the rectifier comes...
As fate would have it earlier today I realized that I think I may have already tried very briefly in the past the two preamp tubes I already had at home that I had marked as "new". I had some noise coming from the amp several years back and bought 3 new preamp tubes and couldn't figure out where the issue was, and so if memory serves I think I may have tried replacing 3 of them at once and found the problem was with only one of the tubes. So I replaced that one and then had these other two ones left over - so two of the new preamp tubes I'm putting in now were very briefly used several years ago. So now I'll be putting in 2 brand new power tubes, 1 brand new rectifier, and 4 brand new preamp tubes and 2 that were used for several hours several years ago. You think this will be a problem in any way?

 

[gene12586]

FWIW, if the rectifier tube that is in there is any good, then I see no reason to worry, or even replace it.. Rectifier tubes simply convert the AC to DC. They don't even process the audio at all. Any changes in the "sound" would be due to the ability of the tube to maintain sufficient and constant voltage for the other tubes, especially under high demand.

I've only changed 1 rectifier tube in the past 10 or more years. I've changed several sets of power tubes and several preamp tubes over the years. Power tubes were done in matched pairs or quads as appropriate. Preamp tubes were replaced as needed, usually for becoming microphonic in combo amps. Tap on the tube, if it goes ZINGGG, pull it and put in a new one. Those little grid wires can bang around when you're cranking through a speaker 6 inches away. They get noisy.

50 years ago, we just went down to Radio Shack or Walgreens, bought a couple of tubes for $3 a pop "just in case" and off we went. Our bassist once blew out his set of 6550s in his Traynor amp during a dance. At break, he ran down to the drug store a couple blocks away, bought 4 tubes, came back and threw them in. (yeah, they sold tubes in drug stores... even had tube testers in a lot of them) We didn't bother with matching or biasing or anything. Plug them in and go!

Thanks for the reply. See my response to Dave.

 

[ecc83]

As I said, valves CAN just last 5 minutes or decades especially pre amp valves. A day, week or month in the life of a valve is nothing. People tend to think of them like the old incandescent lamps we had, "1000 hours" then pop! The one failure mode you will hardly ever see is an O/C valve filament.

Now, before you fit your new set of bottles number them with a Sharpy and the chassis and note the date in your diary.

Dave.

 

[TalismanRich]

. So now I'll be putting in 2 brand new power tubes, 1 brand new rectifier, and 4 brand new preamp tubes and 2 that were used for several hours several years ago. You think this will be a problem in any way?

Other than emptying your pockets of a significant amount of $$$, I see no issue. Was there a problem with the current tubes that needed fixing, or is this just a " I probably should change the tubes " issue?

 

[gene12586]

Other than emptying your pockets of a significant amount of $$$, I see no issue. Was there a problem with the current tubes that needed fixing, or is this just a " I probably should change the tubes " issue?

Thanks, good to hear.
Both of the above. Outside of the one tube that I replaced several years back, all the other tubes had been in there since I bought the amp years ago. And then on top of that I started getting some annoying sounds in recent months. So good time for a change methinks.

 

[rob aylestone]

A group I am involved with were donated a pile of historic kits from a collection, and we had to move loads of junk. The guy who had passed away had a collection of valve testers - and they were programmable! Huge boxes of paxolin type cards with holes cut in them and long different length 'fingers' - each one with a valve (tube) type printed on it. These plug in cards set the tester parameters to the factory specs and you could test each one against the proper performance. Amazing, but HUGE! We found boxes and boxes of the cards. I guess a collector would have loved them!