crash cours on tube amps

[Razman]

so i have an oppurtunity to trade for a vintage fender bassman 100. I just dont know a ton about tube amps. anyone have like a tube amp 101 they can share (or link to me)

Thanks!

No one has really talked about how you use a tube amp in a live situation. Depending on how your tube amp functions under load or at it's limits, you can adjust by using the appropriate number of speakers to get the correct volume and the correct sound. With my Mesa 400, by using less speakers and turning it up more I can get to its angry tone without blowing out eardrums.

For more clean volume, add speaker cabs (matching the impedance, of course).

Enjoy!

speaking of pawn shops I was at a charity sale yesterday and I got a Trace Elliot V4 head for 200 bux. I've never seen one before. I turned it over and saw the 4 Kt88's (assuming someone didn't put 6550's in it) and told the girl to put a sold sticker on it, now please.
I've been told it's a "pre-Gibson." still made in England which is apparently good. And apparently a bit rare, especially the v6's and v8's. Anybody used one?

Absolute junk! I will spare you a lot of pain and anguish by PM'ing you my address and FedEx account number so you can save yourself from that thing. Punish someone like me with it!

Raz

 

[BassmanPaul]

@drewphishes please take the time to correct the spelling in the title. As it is it’s hurting my eyeballs!!

 

[Old Garage-Bander]

@drewphishes please take the time to correct the spelling in the title. As it is it’s hurting my eyeballs!!

Yeah man! It's spelled Coors!

 

[Munjibunga]

Not really. They don't determine the voltage anyway, and the max plate voltage spec is same as EL34.

So what do you consider high plate voltage?

 

[Old Garage-Bander]

So what do you consider high plate voltage?

Anything that hurts you when you touch it.

Let's do a scientific study!
In which group would you like to be?
Test or control?

 

[agedhorse]

The "standby switch" is a complicated yet simple device. Is it necessary? Maybe, for some designs and maybe not for others.

Historically, with tube rectifiers (especially indirectly heated), the tube structure's temperature ramped up via the heaters before the rectifier started conducting so the turn-on was soft(ish) and naturally delayed. The advantage of any type of delayed application of high voltage to the power tube is a more gradual expansion and thermal equilibrium. Perhaps you have heard power tubes make (mechanical) noise as they warm up, this is due to all the structures expanding when heating (and contracting when cooling).

The issue of potential cathode stripping is an interesting one, not really even a potential issue with tube rectifiers but possibly a problem using solid state rectifiers... especially when amps are turned on and off a lot.

I looked back into some of my historical documents, I haven't really thought about this for years, and looked at some of the Altec and Ampex power amps because they were designed for long lifespan and do not have standby switches. What is different about these is the conservative voltages that the power tubes are operated at, and in the case of the Ampex, the screens have their own supply that run about 60% of the plate voltage. Also, solid state rectifiers at those times (where solid state were used ) were selenium types which by nature are fairly squishy compared with silicon rectifiers commonly used today. All of these elements served to improve lifespan (at the tradeoff of reduced power), and it was not uncommon to see 5,000 to as much as 10,000 hours on a set of power tubes. This was important because theatre sound systems typically operated 10-12 hours/day, every day. Another aspect of such operation is the relatively small number of power-ups and downs over the tube's operating life.

With today's guitar amps operating at stupid-high plate voltages, and lots of power-up/down cycles, the argument for keeping the power tubes hot while swapping guitars, going on a short break, messing with pedal board wiring certainly makes for a compelling convenience. With capacitive buffering of the plate supply (or even better, a ramp-up circuit in the B+) this minimizes the step function of voltage on the plates.

Is it "necessary", probably not in the strictest sense, but it can be helpful under the conditions that SOME tube amps might see in the wild.

If I were to design a tube power amp today, I might consider more active management of the supplies... ramp-up/down of the B+ and maybe screen supplies in conjunction with heater timing, and an audio mute switch in place of the HV standby... but I would also be wary of running power tubes within an inch of their lives too. I just might consider eliminating the standby switch (replacing with a "less conventional" mute switch in these applications and would feel ok about it.

 

[BassmanPaul]

Yeah man! It's spelled Coors!

Yuck! If it ain’t Keiths it’s nowt!

 

[Old Garage-Bander]

Yuck! If it ain’t Keiths it’s nowt!

Keith Stone?

 

[Old Garage-Bander]

The "standby switch" is a complicated yet simple device. Is it necessary? Maybe, for some designs and maybe not for others.

Historically, with tube rectifiers (especially indirectly heated), the tube structure's temperature ramped up via the heaters before the rectifier started conducting so the turn-on was soft(ish) and naturally delayed. The advantage of any type of delayed application of high voltage to the power tube is a more gradual expansion and thermal equilibrium. Perhaps you have heard power tubes make (mechanical) noise as they warm up, this is due to all the structures expanding when heating (and contracting when cooling).

The issue of potential cathode stripping is an interesting one, not really even a potential issue with tube rectifiers but possibly a problem using solid state rectifiers... especially when amps are turned on and off a lot.

I looked back into some of my historical documents, I haven't really thought about this for years, and looked at some of the Altec and Ampex power amps because they were designed for long lifespan and do not have standby switches. What is different about these is the conservative voltages that the power tubes are operated at, and in the case of the Ampex, the screens have their own supply that run about 60% of the plate voltage. Also, solid state rectifiers at those times (where solid state were used ) were selenium types which by nature are fairly squishy compared with silicon rectifiers commonly used today. All of these elements served to improve lifespan (at the tradeoff of reduced power), and it was not uncommon to see 5,000 to as much as 10,000 hours on a set of power tubes. This was important because theatre sound systems typically operated 10-12 hours/day, every day. Another aspect of such operation is the relatively small number of power-ups and downs over the tube's operating life.

With today's guitar amps operating at stupid-high plate voltages, and lots of power-up/down cycles, the argument for keeping the power tubes hot while swapping guitars, going on a short break, messing with pedal board wiring certainly makes for a compelling convenience. With capacitive buffering of the plate supply (or even better, a ramp-up circuit in the B+) this minimizes the step function of voltage on the plates.

Is it "necessary", probably not in the strictest sense, but it can be helpful under the conditions that SOME tube amps might see in the wild.

If I were to design a tube power amp today, I might consider more active management of the supplies... ramp-up/down of the B+ and maybe screen supplies in conjunction with heater timing, and an audio mute switch in place of the HV standby... but I would also be wary of running power tubes within an inch of their lives too. I just might consider eliminating the standby switch (replacing with a "less conventional" mute switch in these applications and would feel ok about it.

Did you work for Ampex?

 

[Bigbri]

No one has really talked about how you use a tube amp in a live situation. Depending on how your tube amp functions under load or at it's limits, you can adjust by using the appropriate number of speakers to get the correct volume and the correct sound. With my Mesa 400, by using less speakers and turning it up more I can get to its angry tone without blowing out eardrums.

For more clean volume, add speaker cabs (matching the impedance, of course).

Enjoy!

Absolute junk! I will spare you a lot of pain and anguish by PM'ing you my address and FedEx account number so you can save yourself from that thing. Punish someone like me with it!

Raz

I hate to tell you this but it turned out to be a v6 with all the original tubes. Considering that, I just couldn't do all that harm to you. The v4 maybe, but the v6 I would worry about all the punitive damages to you.
Just to rub it in......

 

[Bigbri]

A serious device. Simple and done right. I used a V-type preamp for a while.

Just picked it up turned out to be a v6.

 

[Mr. Foxen]

So what do you consider high plate voltage?

Plate tends not to be where trouble with high voltages occurs, the grids generally have the lower maximum tolerance and are run closer to it in most amps, rarely see amps running close to plate tolerances. It's cathodes in the kilovolts that are what standby is for.

 

[agedhorse]

Did you work for Ampex?

No, I worked in the cinema industry doing equipment service. Most (but not all) of the old Ampex, Altec, RCA and Western Electric equipment had been retired by the time I was servicing this gear. Much of what I serviced was Dolby and UltraStereo processors, JBL and EV speakers, and JBL, BGW and QSC amplifiers. I got my "retirement papers" along with a whole bunch of folks when Regal Entertainment Group purchased the chain I provided service for. Actually, I was one of two that continued on for a couple of months but the writing was on the wall and the Dear John letter was not at all unexpected.

 

[Old Garage-Bander]

No, I worked in the cinema industry doing equipment service. Most (but not all) of the old Ampex, Altec, RCA and Western Electric equipment had been retired by the time I was servicing this gear. Much of what I serviced was Dolby and UltraStereo processors, JBL and EV speakers, and JBL, BGW and QSC amplifiers. I got my "retirement papers" along with a whole bunch of folks when Regal Entertainment Group purchased the chain I provided service for. Actually, I was one of two that continued on for a couple of months but the writing was on the wall and the Dear John letter was not at all unexpected.

Ah OK. I just spent a lot of time slinging video tape on Ampex quad machines. Interspersed with a little bit of trying to keep them running. The try wasn't so much that they needed a lot of work. I just wasn't very good at it.

 

[ahc]

OP, there's a couple other things about tube amps you should know:

1. If you're not an experienced tech type of guy, don't go pokin' around inside a tube amp. There are lethal voltages inside so keep your hands to yourself.

2. Changing preamp tubes (usually the small ones) if necessary is safe. Changing the power tubes is safe, but see #3.

3. When power tubes (usually the big ones) are changed, its necessary to check and adjust the bias of the tubes for best performance and tube life. This is usually best done by a tech unless you know what you're doing. When changing the power tubes you would want to use a "matched set". These are tubes that have been tested to have similar performance characteristics. Tubes can vary so this is a good idea.

4. If your amp has both a gain and master volume there's two types of distortion available in an all tube amp:
preamp distortion (crank the gain and use the master to control volume) and power amp distortion (crank the master and use the gain to control volume). For max hairyness, everything on "Spinal Tap 11". For clean tones, mix and match as necessary/desired.

A tube amp in good working order will work for a very long time with no problems. I gigged the crap outta several different ones for many years with no trouble.

 

[Bigbri]

OP, there's a couple other things about tube amps you should know:

1. If you're not an experienced tech type of guy, don't go pokin' around inside a tube amp. There are lethal voltages inside so keep your hands to yourself.

2. Changing preamp tubes (usually the small ones) if necessary is safe. Changing the power tubes is safe, but see #3.

3. When power tubes (usually the big ones) are changed, its necessary to check and adjust the bias of the tubes for best performance and tube life. This is usually best done by a tech unless you know what you're doing. When changing the power tubes you would want to use a "matched set". These are tubes that have been tested to have similar performance characteristics. Tubes can vary so this is a good idea.

4. If your amp has both a gain and master volume there's two types of distortion available in an all tube amp:
preamp distortion (crank the gain and use the master to control volume) and power amp distortion (crank the master and use the gain to control volume). For max hairyness, everything on "Spinal Tap 11". For clean tones, mix and match as necessary/desired.

A tube amp in good working order will work for a very long time with no problems. I gigged the crap outta several different ones for many years with no trouble.

I think the v series have LED's for easy biasing.

 

[agedhorse]

Ah OK. I just spent a lot of time slinging video tape on Ampex quad machines. Interspersed with a little bit of trying to keep them running. The try wasn't so much that they needed a lot of work. I just wasn't very good at it.

The father of a guy I went to school with was high up in the Ampex corporate structure and was involved with the whole ATR/VTR division. I remember the principles of the quad machines as the precursor of helical scan, a way to increase the relative tape speed by going vertical (actually diagonal) in stripes.

I repaired a few of the ATR data recorders and multitrack audio machines back in the late 70's and early 80's, but there was no real money in it (for me). I do remember the tape drive motor servo amplifier being a big 'ol low frequency power amp using 6550's... very impressive.

 

[Old Garage-Bander]

The father of a guy I went to school with was high up in the Ampex corporate structure and was involved with the whole ATR/VTR division. I remember the principles of the quad machines as the precursor of helical scan, a way to increase the relative tape speed by going vertical (actually diagonal) in stripes.

I repaired a few of the ATR data recorders and multitrack audio machines back in the late 70's and early 80's, but there was no real money in it (for me). I do remember the tape drive motor servo amplifier being a big 'ol low frequency power amp using 6550's... very impressive.

Yup, we had a 1000 (flat deck) that still had the tube servo system, when I started.
I cut my teeth on the 1000, 1100 and I did a lot of manually timed electronic editing on those.
My boss at the time, had experience with physically splicing quad tape. He did a physical splice one day at work, just to see if he still had "it."
We then "upgraded" to the Ampex one inch, helical scan machines.
The actual machines that we got were part of a shipment that was supposed to go to the 1980 Olympics.
When the US boycotted, two of them got re-routed to us.
We still have a working 1200. Occasionally someone has something on quad they want dubbed down.

 

[Korladis]

The "standby switch" is a complicated yet simple device. Is it necessary? Maybe, for some designs and maybe not for others.

Historically, with tube rectifiers (especially indirectly heated), the tube structure's temperature ramped up via the heaters before the rectifier started conducting so the turn-on was soft(ish) and naturally delayed. The advantage of any type of delayed application of high voltage to the power tube is a more gradual expansion and thermal equilibrium. Perhaps you have heard power tubes make (mechanical) noise as they warm up, this is due to all the structures expanding when heating (and contracting when cooling).

The issue of potential cathode stripping is an interesting one, not really even a potential issue with tube rectifiers but possibly a problem using solid state rectifiers... especially when amps are turned on and off a lot.

I looked back into some of my historical documents, I haven't really thought about this for years, and looked at some of the Altec and Ampex power amps because they were designed for long lifespan and do not have standby switches. What is different about these is the conservative voltages that the power tubes are operated at, and in the case of the Ampex, the screens have their own supply that run about 60% of the plate voltage. Also, solid state rectifiers at those times (where solid state were used ) were selenium types which by nature are fairly squishy compared with silicon rectifiers commonly used today. All of these elements served to improve lifespan (at the tradeoff of reduced power), and it was not uncommon to see 5,000 to as much as 10,000 hours on a set of power tubes. This was important because theatre sound systems typically operated 10-12 hours/day, every day. Another aspect of such operation is the relatively small number of power-ups and downs over the tube's operating life.

With today's guitar amps operating at stupid-high plate voltages, and lots of power-up/down cycles, the argument for keeping the power tubes hot while swapping guitars, going on a short break, messing with pedal board wiring certainly makes for a compelling convenience. With capacitive buffering of the plate supply (or even better, a ramp-up circuit in the B+) this minimizes the step function of voltage on the plates.

Is it "necessary", probably not in the strictest sense, but it can be helpful under the conditions that SOME tube amps might see in the wild.

If I were to design a tube power amp today, I might consider more active management of the supplies... ramp-up/down of the B+ and maybe screen supplies in conjunction with heater timing, and an audio mute switch in place of the HV standby... but I would also be wary of running power tubes within an inch of their lives too. I just might consider eliminating the standby switch (replacing with a "less conventional" mute switch in these applications and would feel ok about it.

Modern guitar amps operate at notably high plate voltages compared to those of ye olde days?

 

[Old Garage-Bander]

Modern guitar amps operate at notably high plate voltages compared to those of ye olde days?

Uh, define "modern." Many modern amps don't have plates to supply.