My PP GE VT4C Amp was going to be an almighty guitar amp, but apart from the drivers issues that I face, with a B+ of 1150 the tube is way to slow!
ie; strike a string, and after a longg time, you hear the note.
This maybe fine if your source is vinyl or a cd, but when I plug in a guitar, it feels like driving a huge under-powered truck instead of a responsive amp.
This gets worse incorporating multiple driver stages as you need to with a 211.
Maybe the B+ is too low, I heard some ppl put 2k onto the plate...
ie; strike a string, and after a longg time, you hear the note.
This maybe fine if your source is vinyl or a cd, but when I plug in a guitar, it feels like driving a huge under-powered truck instead of a responsive amp.
This gets worse incorporating multiple driver stages as you need to with a 211.
Maybe the B+ is too low, I heard some ppl put 2k onto the plate...
This is a surprise since most of the coments that I get about PowerDrive praise the attack and the dynamics. I have played my guitar through my 845SE amp several times, and there is no delay, in fact it is a fast and dynamic amp. It is a single ended amp running 1100 volts. I have tried it with 211's (similar to a VT4-C) but I prefer the sound of 845's when playing CD's (often highly dynamic rock music) so that is what I usually have in the amp.
A mosfet with a lot of gate capacitance can cause a dark muddy sound. What kind of fets did you try? If you can, post your schematic (including the PowerDrive circuit) so we can look at it. I will reply, but it may be delayed due to tropical storm Ernesto, and the associated media (TV) induced hysteria. We were out of work for 2 days, and it will take several more days for things to return to normal, although the storm itself caused little if any damage.
I read, with interest about a push pull guitar amp using 4 X 813's that put out 1 killowatt. I have collected some 813's, if I can find an OPT, I could be tempted to make some serious sound.
I too have heard fast and quick sounding 211/845 based amplifiers, and I have also heard an amplifier based on Tubelab's powerdrive design, and it was very quick, detailed, dynamic and powerful. IMHO for driving an 845 this has got to be one of the best ways to do it, particularly if A2 operation for higher power is contemplated.
Svetlana are you using tubelab's powerdrive circuit or something else? Sharing circuit design details might help us to understand what is going on.
What operating point have you chosen for the output tube? Is it operating in a range that would be considered appropriate for class A operation or do you have the bias cranked way up so that it is almost cut off? Is it PP or SE, if SE this would be a receipe for massive distortion of course..
The 211 and 845 are pretty fragile so I wouldn't necessarily recommend using an amplifier based on either of these tubes on the road..
Svetlana are you using tubelab's powerdrive circuit or something else? Sharing circuit design details might help us to understand what is going on.
What operating point have you chosen for the output tube? Is it operating in a range that would be considered appropriate for class A operation or do you have the bias cranked way up so that it is almost cut off? Is it PP or SE, if SE this would be a receipe for massive distortion of course..
The 211 and 845 are pretty fragile so I wouldn't necessarily recommend using an amplifier based on either of these tubes on the road..
I (and others) have found that the filaments in most transmitting tubes are reasonably robust when new. After a few dozen turn on cycles they become very brittle. 211's, 845's and 833A's are particularly bad. And roadies are not always nice to equipment, especially heavy equipment. That is one on the reasons (and the time factor) that I haven't built the 833A SE guitar amp. I have had a few requests for it, but I don't think that the average user would be happy with the reliability, not to mention the 2000 volts!
George, I get a kick out your high power guitar amps. But why so much power? Ever since I first heard a Fender Twin Reverb nearly blow the windows out of the room when I cranked it to "10", I figured it was enough for any small venue. Are you scheduled to play in Madison Square Garden?
My guitar amp has four 7591s (an unsual Audio Guild Panaramic). It's too much. A future project is an EL84 guitar amp which could be pushed into output stage overdrive without deafening the neighbors.
PS Awaiting Ernesto as you must be. So far nothing's happening, but I'm north of you. Hope you're doing OK.
My guitar amp has four 7591s (an unsual Audio Guild Panaramic). It's too much. A future project is an EL84 guitar amp which could be pushed into output stage overdrive without deafening the neighbors.
PS Awaiting Ernesto as you must be. So far nothing's happening, but I'm north of you. Hope you're doing OK.
That is unusual. I thought that I had the only one of those left in captivity. I bought mine about 10 years ago at the local swap shop flea market for $35. The guy selling it swore that it worked. When I got it home and opened it up it looked very clean, so I plugged it in. It did indeed, and still does work very well. It is the only amp that I use on a regular basis. Very nice bluesey sound. I have an old Gibson Skylark that uses a single ended 6AQ5 that gets played sometimes. I also have a 150 watt SS amp that my daughter left behind when she moved out. It hasn't been turned on in 5 years.
I build the big stuff for "bragging rights", or for a customer who wants one, but other than showing off I rarely use it. My hearing is bad enough already. Of all of the guitar amps that I have built for others, the most popular were the "Turbo Champs" that I built several years ago. They made about 8 to 10 watts at full tilt with a KT88 installed in pentode mode. These were usually used in small club gigs or for recording. The user could put in a 6V6 and a 5Y3 and get a sweet distorted sound without being too loud, or an EL34 or KT88 for a relatively clean sound in triode mode. I have also built a few of the typical push pull 2 or 4 tube style amps for the loud crowd.
Ernesto, passed through early this morning. Mild winds, maybe 4 or 5 inches of rain, no flooding. The local TV started showing pictures from Wilma and Katrina on Saturday causing 2 hour gas lines and empty grocery stores, but that was the worst of it. It is still raining, but nothing worse than a typical rainy day. Motorola was closed for two days, so I will probably have to work this weekend to catch up.
Its not the dynamics that is an issue for me, it the delay at which things get presented at my speaker.
I suspect the or delay (lack of speed), of the 211's has to do with the area of the plate, the distance between the plate and grid, and the B+ applied. Possibly higher B+ and the electrons will get there quicker?
Hi, Tube lab, the powerdrive was the exact same circuit on your page, with the exact same mosfets.
I did not use a 45 to drive it, the drive came straight from my (oil) choke loaded 6sl7 phase splitter. (My 211's are running in push pull, B+1125)
I paid particular attention to the supplies (oil chokes, high speed diodes, oil caps).
Mosfets were mounted on a large/medium sized heat sink.
The -400vdc supply that you use, you said only has to be high enough (voltage) to completely cut off the tube, I used -150.
All supplies could deviled good current.
Initial impressions from my custom all tube guitar pre-amp (please please take this as constructive, or inexperienced munting on my part):
On a clean channel, all the harmonics that gave it the magic disappeared, sound was not as deep, the 3d effect went; it seemed to present a different "format" to the grid of the 211.
On the hi-gain channel, I immediately noticed a buzzing sound that was never there before. Instead of a warm thunder, it was like someone inserted a buzzsaw into the mix (think Marshall valvestate)
Maybe im hearing this because:
1: my 211 psu is impeccable; a CLC, mercury vapor rectifies, high current oil filled choke and NOS GE Pyranol oil Caps.
2: my source is impeccable; I designed the tube preamp with a very very accurate PP RCA 6L6GC triode amp.
Maybe I didn't mess with it enough.
I love the tone of the 211's, it seems I can present the grid with a very complex mixture of tones and harmonics, and it faithfully deals with them all without breaking a sweat. With a good PSU, I can see why the hi-fi ppl love them. (and im only using the GE's)
If only they were easier to drive, and faster!
I agree with tubelab? regarding the 211 grids, one of mine is noisy and rattles and its a pain in the ***.
I'd love to try a 813 amp, those pentode look so bad ***
I suspect the or delay (lack of speed), of the 211's has to do with the area of the plate, the distance between the plate and grid, and the B+ applied. Possibly higher B+ and the electrons will get there quicker?
Hi, Tube lab, the powerdrive was the exact same circuit on your page, with the exact same mosfets.
I did not use a 45 to drive it, the drive came straight from my (oil) choke loaded 6sl7 phase splitter. (My 211's are running in push pull, B+1125)
I paid particular attention to the supplies (oil chokes, high speed diodes, oil caps).
Mosfets were mounted on a large/medium sized heat sink.
The -400vdc supply that you use, you said only has to be high enough (voltage) to completely cut off the tube, I used -150.
All supplies could deviled good current.
Initial impressions from my custom all tube guitar pre-amp (please please take this as constructive, or inexperienced munting on my part):
On a clean channel, all the harmonics that gave it the magic disappeared, sound was not as deep, the 3d effect went; it seemed to present a different "format" to the grid of the 211.
On the hi-gain channel, I immediately noticed a buzzing sound that was never there before. Instead of a warm thunder, it was like someone inserted a buzzsaw into the mix (think Marshall valvestate)
Maybe im hearing this because:
1: my 211 psu is impeccable; a CLC, mercury vapor rectifies, high current oil filled choke and NOS GE Pyranol oil Caps.
2: my source is impeccable; I designed the tube preamp with a very very accurate PP RCA 6L6GC triode amp.
Maybe I didn't mess with it enough.
I love the tone of the 211's, it seems I can present the grid with a very complex mixture of tones and harmonics, and it faithfully deals with them all without breaking a sweat. With a good PSU, I can see why the hi-fi ppl love them. (and im only using the GE's)
If only they were easier to drive, and faster!
I agree with tubelab? regarding the 211 grids, one of mine is noisy and rattles and its a pain in the ***.
I'd love to try a 813 amp, those pentode look so bad ***
Well, if your looking for tough xmit tubes, the GI-7bT is built for tank service. 
Vibration loads:
frequency, Hz: 5-600
acceleration, m/s²: 59
Multiple loads with acceleration, m/s²: 342
Single impacts with acceleration, m/s²: 1,465
Linear loads with acceleration, m/s²: 490
Not a DHT and Ive no idea what it sounds like though.
Vibration loads:
frequency, Hz: 5-600
acceleration, m/s²: 59
Multiple loads with acceleration, m/s²: 342
Single impacts with acceleration, m/s²: 1,465
Linear loads with acceleration, m/s²: 490
Not a DHT and Ive no idea what it sounds like though.
What a load of crap.
Imagine driving a car, and there was a delay in the time it took from when you pressed your foot on the the break, to the time the break started to work, and there was a delay from the time you turned the steering wheel, to the time when the wheels actually moved.
It would be a pretty horrible car.
I once read of a famous guitarist left tube amps and went to solid state devices because of the delays (speed).
I too will build a BJT amp for this reason.
But, I still want my pig 211, with the glorious tone, to rock.
I think I will look at pentode drivers and interstages.
Imagine driving a car, and there was a delay in the time it took from when you pressed your foot on the the break, to the time the break started to work, and there was a delay from the time you turned the steering wheel, to the time when the wheels actually moved.
It would be a pretty horrible car.
I once read of a famous guitarist left tube amps and went to solid state devices because of the delays (speed).
I too will build a BJT amp for this reason.
But, I still want my pig 211, with the glorious tone, to rock.
I think I will look at pentode drivers and interstages.
Svetlana said:
That would be as horrible car indeed, but your use of the word "delay" cannot properly describe what is happening in your tube amp, at least from an engineering perspective. Perhaps your amp is rolled off in the highs and it is harder for you to hear the leading edge of your stuck note. That might make you think you're hearing a delay, but if you were to place a scope on the input and output you'd see that the output starts to react almost instantaneously to the input. Unless you had a digital delay connected, but you didn’t mention that. Just physics...
There is some debate about the delay in Svetlana's amplifier. I agree that the electrical propagation delay through any audio amplifier (HiFi or MI) should be inaudible (by several orders of magnitude). However, I have built guitar amplifiers that exhibit the same sort of effect that Svetlana describes. This happened (at least in my case) when the amplifier was heavilly overdriven by blasting its input with a few daisy chained effects pedals. It worked OK when driven with a raw guitar set on 5. I had spent quite some time tweaking parts to get a good sustain.
What was going wrong? The biggest culprit was too large of coupling capacitors, and a few other factors that added up to bias shift. If you whacked the amp with enough signal to drive it into serious distortion it would respond, the first time. After that the the beginning of each successive note would get chopped off. We all have heard about "blocking distortion" that gets generated as the output tube's grid gets driven positive enough to drain some of the charge off of the coupling cap. As soon as the note stops the the output tube goes into cut off. I new about this and took proper measures to prevent it, but in this case it was the 12AU7 that was chopping up my music. Reducing the value of the coupling caps, and grid resistors fixed this amp. I have seen similar effects when I intentionally built too much sag into the power supply.
If the delay is as bad as you say, it should be easy to chase down with a scope. Put one channel on the input, and work your way down the amp chain with the other channel. Compare the initial attack of the two channels. They should be virtually identical except for the gain. I routinely do this with my amp designs. I also measure stage by stage gain and phase VS frequency. I did this when I built this amp (using PowerDrive sucessfully in a high power guitar amp)
http://www.tubelab.com/833SE.htm
This may or may not relate to your situation. I can offer a few suggestions. If you want to try a pentode driver, look at TV sweep tubes. These have the highest peak current capacity of any available receiving tube. I have found that to make a guitar amp for resale, you must use tubes that the average musician can buy at a music store. This is obviously not the case with your amp, so TV tubes are worth looking at. I was looking at pentode cathode followers before I started using mosfets. The sweep (horizontal output) tubes excelled here. The best was a 6LW6, then 6JE6 and similar sized tubes. I also used the 6AV5 in less demanding circuits. I am not sure what is available in your area, but I am sure that there is something. The vertical output, dissimilar twin triodes, as previously mentioned are also useful.
In your other thread you mentioned trying a DHT and an interstage transformer. For a guitar amplifier you don't need an ultra expensive transformer. The expense in IT's is getting the lowest (20 to 40Hz) and highest (10 to 20 KHz) octaves right. You don't even use these extremes in a guitar amp. Also for this application, a triode wired EL34 or even a 6L6 sounds good. I have been experimenting with the $20 universal driver transformer from Triode Electronics. The low cost Hammonds should also work in this application.
Actually, mine is called an Ultraflex. From what (little) I could find on the web it is the same amp. I was about to ask you if you had a schematic. I have found no information about this amp on the web. I can remember seeing an amp like this in the music store where I took guitar lessons when I was in high school. That was what prompted me to buy this one and carry it about 1/4 mile out to my car. I also have a Guild guitar, which resembles a Gibson SG. As the salesman would tell prospective customers, The Audio Crafters Guild, or Audio Guild, or just Guild (all 3 names were used) was formed by people that came from Fender and Gibson to form the Guild. They made guitars for quite a while. If they actually made this amp, they didn't make it for long.
I took mine apart when I got it and figured out that it was really two amps in one. The preamps feed into two 7591 P-P amps through the "Ultraflex" circuit which seems to be a crossover network. The Ultraflex Balance control is like the balance control on a stereo. It controls the relative volume of the two power amps. The power amps look identical, except for the output transformers and speakers. It appears to have been made in 1967. This is all I have found on the web:
http://www.vibroworld.com/magnatone/PAN_unknown.html
What was going wrong? The biggest culprit was too large of coupling capacitors, and a few other factors that added up to bias shift. If you whacked the amp with enough signal to drive it into serious distortion it would respond, the first time. After that the the beginning of each successive note would get chopped off. We all have heard about "blocking distortion" that gets generated as the output tube's grid gets driven positive enough to drain some of the charge off of the coupling cap. As soon as the note stops the the output tube goes into cut off. I new about this and took proper measures to prevent it, but in this case it was the 12AU7 that was chopping up my music. Reducing the value of the coupling caps, and grid resistors fixed this amp. I have seen similar effects when I intentionally built too much sag into the power supply.
If the delay is as bad as you say, it should be easy to chase down with a scope. Put one channel on the input, and work your way down the amp chain with the other channel. Compare the initial attack of the two channels. They should be virtually identical except for the gain. I routinely do this with my amp designs. I also measure stage by stage gain and phase VS frequency. I did this when I built this amp (using PowerDrive sucessfully in a high power guitar amp)
http://www.tubelab.com/833SE.htm
This may or may not relate to your situation. I can offer a few suggestions. If you want to try a pentode driver, look at TV sweep tubes. These have the highest peak current capacity of any available receiving tube. I have found that to make a guitar amp for resale, you must use tubes that the average musician can buy at a music store. This is obviously not the case with your amp, so TV tubes are worth looking at. I was looking at pentode cathode followers before I started using mosfets. The sweep (horizontal output) tubes excelled here. The best was a 6LW6, then 6JE6 and similar sized tubes. I also used the 6AV5 in less demanding circuits. I am not sure what is available in your area, but I am sure that there is something. The vertical output, dissimilar twin triodes, as previously mentioned are also useful.
In your other thread you mentioned trying a DHT and an interstage transformer. For a guitar amplifier you don't need an ultra expensive transformer. The expense in IT's is getting the lowest (20 to 40Hz) and highest (10 to 20 KHz) octaves right. You don't even use these extremes in a guitar amp. Also for this application, a triode wired EL34 or even a 6L6 sounds good. I have been experimenting with the $20 universal driver transformer from Triode Electronics. The low cost Hammonds should also work in this application.
Actually, mine is called an Ultraflex. From what (little) I could find on the web it is the same amp. I was about to ask you if you had a schematic. I have found no information about this amp on the web. I can remember seeing an amp like this in the music store where I took guitar lessons when I was in high school. That was what prompted me to buy this one and carry it about 1/4 mile out to my car. I also have a Guild guitar, which resembles a Gibson SG. As the salesman would tell prospective customers, The Audio Crafters Guild, or Audio Guild, or just Guild (all 3 names were used) was formed by people that came from Fender and Gibson to form the Guild. They made guitars for quite a while. If they actually made this amp, they didn't make it for long.
I took mine apart when I got it and figured out that it was really two amps in one. The preamps feed into two 7591 P-P amps through the "Ultraflex" circuit which seems to be a crossover network. The Ultraflex Balance control is like the balance control on a stereo. It controls the relative volume of the two power amps. The power amps look identical, except for the output transformers and speakers. It appears to have been made in 1967. This is all I have found on the web:
http://www.vibroworld.com/magnatone/PAN_unknown.html
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