Solid state/class d vs tube amps

[agedhorse]

Cats can help too, as you have discovered. There is an acoustic term called "dead cats" which represent a colloquial unit of absorption.

 

[mobdirt]

These days I'm using an api tranzformer balanced out going into a crown xls1500, couldn't ask for more.

 

[xk49w]

There are 2 nested feedback loops plus a global feedback loop in that amp, with high impedance phase splitter combined with grid stoppers and hefty grid to cathode capacitance, my guess is that they had some real stability problems under higher gain conditions. 220pF is about 100x the typical grid capacitance to the cathode, and the high drive impedance is going to cause some significant HF rolloff. Maybe the feedback will improve this a bit, like stealing from Peter to pay Paul.

I've never understood putting tone and volume controls inside a global feedback loop. I've seen other designs that did this too, but it just never seemed like a good idea to me. It's going to create interesting nonlinearities when it tries to take those effects out. Maybe that's the point. Whatever works I guess.

 

[agedhorse]

I've never understood putting tone and volume controls inside a global feedback loop. I've seen other designs that did this too, but it just never seemed like a good idea to me. It's going to create interesting nonlinearities when it tries to take those effects out. Maybe that's the point. Whatever works I guess.

The presence control is not really a tone control, since it changes the damping versus frequency curve also. On SOME amps it can work very well, on others not so good. Everything do do to a feedback loop affects stability too.

The heavy compensation suggests that there may have been some stability issues.

 

[beans-on-toast]

Since the feedback bone is connected to the transformer bone which is connected to the speaker bone, the whole system is part of the presence. A change of speaker can affect how well presence works. When people start mixing amps and cabs you never know how it will affect the performance of the controls.

 

[BadExample]

Since the feedback bone is connected to the transformer bone which is connected to the speaker bone

now hear the word of old horse.

 

[AE1]

I believe the amp you referenced, is a class AB. I found a Garnet, that possibly could be a class B, the BTO PA260, The last preamp tube is a 6sn7, with both triodes wired in parallel, and the combined plates are feeding what looks like a center tap choke. If you give us a model, it will help.

Here is the schematic for the Garnet B260D and L260D GUITAR amps

There should be similar models for bass but without the tremolo

http://garnetamps.com/history.htm

They nicely show the transformer phase inversion drive system, grid stopper resistors (270 Ohms) and screen resistors (470 Ohms)

The parallel connected 6SN7 is used to achieve a higher signal drive power into the transformer. Could have been a triode connected 6V6GT, 6L6GT, EL34 or similar but that would require significantly more B+ DC current, higher DC rated transformer primary and filter choke - the 6SN7 is a best fit compromise solution and most likely does the job well

The voltage divider half-wave bias supply into 64 uF and the tremolo circuit could result in a time delay in attaining bias voltage at startup. Is a low current supply - could be improved. Other brands use only 10 uF to speed up the process but that results in more ripple in the bias supply. This system is fine if the standby switch powers-on after the power tubes warm up.

The filter caps suggest the B+ is at least 600 VDC so this is a gutsy amp (maybe 130 watts rms/260Watts peak as the type number implies)

One feature common to PA amps from the 1940's on was the high frequency attenuator across the output transformer - solves a lot of problems. (A full range top end is not needed for guitar or bass amps)

 

[AE1]

Since the feedback bone is connected to the transformer bone which is connected to the speaker bone, the whole system is part of the presence. A change of speaker can affect how well presence works. When people start mixing amps and cabs you never know how it will affect the performance of the controls.

so long as the bigbone does not drop onto your foot

 

[Drgonzonm]

From another schematic your voltages are listed on the left side the -44v is the bias voltage

Here is the schematic for the Garnet B260D and L260D GUITAR amps

There should be similar models for bass but without the tremolo

http://garnetamps.com/history.htm

They nicely show the transformer phase inversion drive system, grid stopper resistors (270 Ohms) and screen resistors (470 Ohms)

The parallel connected 6SN7 is used to achieve a higher signal drive power into the transformer. Could have been a triode connected 6V6GT, 6L6GT, EL34 or similar but that would require significantly more B+ DC current, higher DC rated transformer primary and filter choke - the 6SN7 is a best fit compromise solution and most likely does the job well

The voltage divider half-wave bias supply into 64 uF and the tremolo circuit could result in a time delay in attaining bias voltage at startup. Is a low current supply - could be improved. Other brands use only 10 uF to speed up the process but that results in more ripple in the bias supply. This system is fine if the standby switch powers-on after the power tubes warm up.

The filter caps suggest the B+ is at least 600 VDC so this is a gutsy amp (maybe 130 watts rms/260Watts peak as the type number implies)

One feature common to PA amps from the 1940's on was the high frequency attenuator across the output transformer - solves a lot of problems. (A full range top end is not needed for guitar or bass amps)

View attachment 2873911

 

[agedhorse]

The supply voltage does not in any way indicate what the power might be without knowing the transformer ratio. It could just as easy be 100 watts with a higher primary impedance.

The drive impedance doesn't have to be that low, the transformer could just as easily be 1:1.

The bias supply time constant doesn't matter, it's easily going to be many times faster than the warm-up time of the tubes before conduction begins.

 

[Drgonzonm]

The supply voltage does not in any way indicate what the power might be without knowing the transformer ratio. It could just as easy be 100 watts with a higher primary impedance.

The bias supply time constant doesn't matter, it's easily going to be many times faster than the warm-up time of the tubes before conduction begins.

my post was just to provide reference to the list. (G)voltages are probably plus or minus the 20%.
If you look at the schematic, the bias origin point is not on the secondary side of the PT.

 

[agedhorse]

Since the feedback bone is connected to the transformer bone which is connected to the speaker bone, the whole system is part of the presence. .

I might have to use this in a marketing meeting

 

[BadExample]

I might have to use this in a marketing meeting

Tell them is has a transformador.

 

[agedhorse]

Tell them is has a transformador.

Last time I referred to upgrading the muffler bearing I had to eat lunch alone!

 

[BadExample]

Last time I referred to upgrading the muffler bearing I had to eat lunch alone!

I own TWO disco traps. Precursor to the Supertrapp. A side project to fund the fairly insane inventor trying to make and sell his Airocar. I think @Al Kraft will know of this guy. The first one is a really weird flat can shaped thing known as a "Bug in a Box" for the funky sounds it makes on a dirtbike. The second is now known as a "Vintage Trapp" and all parts are available. The latter is really cool, because I can swap discs and avoid re-jetting for seasons. I used to ride my zuk SP250 year round as long as it was at least 25 F or higher and no freezing rain.

 

[Drgonzonm]

Last time I referred to upgrading the muffler bearing I had to eat lunch alone!

the part is probably used on class d leslies

 

[Al Kraft]

I think @Al Kraft will know of this guy.

You can only be talking about the one and only Paul Moller out of Davis CA. From humble beginnings with the XM-2 and 3 (IIRC) to the latest M400 Skycar.

 

[agedhorse]

I own TWO disco traps. Precursor to the Supertrapp. A side project to fund the fairly insane inventor trying to make and sell his Airocar. I think @Al Kraft will know of this guy. The first one is a really weird flat can shaped thing known as a "Bug in a Box" for the funky sounds it makes on a dirtbike. The second is now known as a "Vintage Trapp" and all parts are available. The latter is really cool, because I can swap discs and avoid re-jetting for seasons. I used to ride my zuk SP250 year round as long as it was at least 25 F or higher and no freezing rain.

I knew Paul Moller, his early shop was located around the corner from my old shop. He was an ME professor at the university I graduated from.

 

[Al Kraft]

I knew Paul Moller, his early shop was located around the corner from my old shop. He was an ME professor at the university I graduated from.

Yep that's him,...he is better known in the academic community as Dr. Paul Moller. IMO he is a visionary and innovator in the aerospace world in the same league as other greats like Kelly Johnson and Burt Rutan.

 

[BadExample]

You can only be talking about the one and only Paul Moller out of Davis CA. From humble beginnings with the XM-2 and 3 (IIRC) to the latest M400 Skycar.

Yup, Andy's neighbor I guess. Made a fortune on the muffler company. IIRC the SuperTrapps made it all the way into the locomotive industry. The bug in the box I stuffed with SS swarf from my lathe, based on the patent, The classic I removed some really stinky stuffing, restuffed with 4T muffler material, after very cautiously brazing on a new nipple, preserving the original 70's JB Bros. sticker on it, then carefully masking and painting it. Then I installed a nice Keihin pumper carb to replace the the CV junk. The used carb had a clogged jet and ate the sticker in 1 minute but it did make the head pipe glow a really purdy red