Suitability of transmitter tubes for musical amplifiers

[Svetlana]

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...

[tubelab.com]

strike a string, and after a longg time, you hear the note.

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.

[kevinkr]

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..

[tubelab.com]

The 211/845 is pretty fragile so I wouldn't necessarily recommend using an amplifier based on this tube 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!

[Brian Beck]

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.

[tubelab.com]

My guitar amp has four 7591s (an unsual Audio Guild Panaramic).

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.

PS Awaiting Ernesto as you must be. So far nothing's happening, but I'm north of you. Hope you're doing OK.

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.

[Brian Beck]

Wow, you have a Panaramic too? I’ll bet mine is in seedier condition than yours. Do you have a schematic for it? I never located one. There is precious little information about this amp or the company on the web.

[Svetlana]

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 ***

[Tweeker]

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.

[Nixie]

When I read the title of transmitter tubes, I thought ceramic forced air cooled stuff, not measly glass radiative cooled ones... zzzZZZ

Come on guys, how about some OTL 3CX800A7 amps...