Not to mention the micro rotary engine generator business.
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Solid state/class d vs tube amps
- Thread starter Sparkl
- Start date
I got the analogy and didn't take you as a meatless freak. We are carnivores!
I've got a couple pounds of Navy beans soaking now, need to get the ham tomorrow!
I hung out with a dude yesterday that just only plays a Markbass LM2, matching 210, and a stock AM Std P.
He has been on that setup since it was all new.
He plays my Jazz 5 with Fralin 10% overwounds thru the Buster and he says "your bass is tuned weird, there's these weird sounds".
I look at him and tell him first it's a 5-string so mute it better, don't mind the tube amp or hot passive pickups.
It's a 5-string, the look on his face was if I'd handed him a crack pipe in church.
I grab his P and plug into my amp and he looks at me like "omg you broke my bass" and says "that sounds weird".
Then I plug his Markbass into the Buster's 15' and turn down the 2 voicing knobs and the guy is turning red.
I thought his LM2 sounded pretty good with a cab that does kinda what the voicing knobs pretend to do.
When I was playing a Mesa RR 215 amps like the LM2 didn't exist so it was kinda fun to see what would happen.
So yeah, lots of people in real life just have "that" setup and nothing else really ever will change bc it deviates from the sound they're used to.
It reminds me of a software engineer I worked with that ate the same packed lunch everyday for 2 years until I left Ireland, was totally odd.
In principle it could, but in this case T1 is shown on the schematic to be 3k - ie 6k per pair of tubes.
What is more relevant is that the tube type is not shown - could be EL34, KT66, KT88 or 6550 or something else
But the Garnet PA260 has an identical schematic and uses EL34 tubes so am happy to stay with that. Two pairs are good for more than 130 watts rms from 500 VDC - similar to some Marshall model specs
That will be a comfort to Garnet amp owners but my concern is that since this is a Class B amp (-44V bias) biased to nearly cutoff it is essential to ensure the bias is in place before plate voltage is applied. Timing is critical because at -20 V bias the plate current approaches 200 mA per tube. 500V x 0.2A = 100 watts dissipation - per tube at zero signal. The modern way is to use a time delay relay in the B+ supply interlocked with the bias supply - a feature common in big vintage PA amps running transmitting tubes.
I would rather be safe than sorry. Murphy's Law says "If something can go wrong it will"
Here is a bias protection system for directly heated filament tubes - is conceptually similar to one for indirectly heated tubes
- Feb 12, 2006
- 60,963
- 5
- 220,655
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Explain how the tube can possibly conduct with the amount of heater time lag presented in all power tubes? The only applications where I have ever seen plate/screen voltages interlocked with bias is on amps that use pre-heated heaters without the bias being present (kind of a dumb idea), not something that and MI amp uses. You are way out there in the weeds on this.
Running 130 watts from a pair of EL34s is going to result in short tube life. Sure it may be possible, but it's not good engineering practice.
IMO, the Garnet designs are great examples of poor engineering. There is a reason most of these circuit elements were never used by the main stream and died in obscurity.
Running 130 watts from a pair of EL34s is going to result in short tube life. Sure it may be possible, but it's not good engineering practice.
IMO, the Garnet designs are great examples of poor engineering. There is a reason most of these circuit elements were never used by the main stream and died in obscurity.
It can help to look at things in context. The Garnet amps were designed by rule of thumb and seat of the pants, as were many designs back in the 60’s. By todays standards, there certainly wasn’t the same level of engineering that went into the designs.
If you looks at the Garnet designs, there was a design evolution over the years. Gar was a radio man. His early designs adopted some of what was found in radios from the 40’s and 50’s. These were long used design elements that he knew, they were used in the amp designs.
In the 60’s players wanted rich distortion. People in bands, well known in the industry, would show up and amps were tweaked and tried on the spot to provide those overdriven sounds. They has something very specific in mind. Amps were designed to operate at or beyond their design limits to produce that sound. Sometimes they sat on the edge of oscillation and caps were added around tubes to help deal with that. Tubes were relatively cheap so tube life wasn’t an issue. It was all about the sound.
Not all their products were designed to operate this way. Many were more general purpose. At the same time Garnet pioneered high gain stages and using relays for switching. Something that others in the industry adopted.
A lot of the products were built point to point. They looked like a rats nest but were done well. The amps were quiet. People that had to repair them sometimes cringed at the thought of having to dig in to them.
If you looks at the Garnet designs, there was a design evolution over the years. Gar was a radio man. His early designs adopted some of what was found in radios from the 40’s and 50’s. These were long used design elements that he knew, they were used in the amp designs.
In the 60’s players wanted rich distortion. People in bands, well known in the industry, would show up and amps were tweaked and tried on the spot to provide those overdriven sounds. They has something very specific in mind. Amps were designed to operate at or beyond their design limits to produce that sound. Sometimes they sat on the edge of oscillation and caps were added around tubes to help deal with that. Tubes were relatively cheap so tube life wasn’t an issue. It was all about the sound.
Not all their products were designed to operate this way. Many were more general purpose. At the same time Garnet pioneered high gain stages and using relays for switching. Something that others in the industry adopted.
A lot of the products were built point to point. They looked like a rats nest but were done well. The amps were quiet. People that had to repair them sometimes cringed at the thought of having to dig in to them.
In some cultures "Perro" is the almost the worst thing you can be called.
Your story just made me remember that beautifull song by Temple of the Dog "Call me a dog".
and some of the parts are hard to find. Some of the design does not pass today's safety standards. (The bias circuit for example, and the death cap. ) To me very few companies were willing to use center tap chokes as phase inverters, and from a cost stand point, the PI choke and the octal tube seems ridiculous) maybe the 260 is a class AB2, but without further evaluation, I'm not not calling it a class B. I don't have the time or the experience to reverse engineer the amp.
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I agree, but that said, the amp in question (PA260, aka BTO chassis, two versions of the schematic posted upthread) has TWO pairs of EL34s.
Garnet may or may not have some of the other shortcomings which you mentioned, but they were no worse at overstating power output than any other tube amp maker of their era.
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If you mean the bias supply sourced from the primary side of the PT - yes, I noticed that too, however some other Garnet models took it from one leg of the secondary.
The octal driver tube was likely a carryover from radio and TV days, and a 6SN7 was pretty common in many older B&W TVs (vertical oscillator ?), I think being superceded by the 12AU7 when the industry went to miniatures.
And I have not seen that choke phase inverter idea used by any other amp maker, as most went right away to the Fender/Marshall/Traynor/etc design, and either a 12AT7 (Fender) or a 12AX7 for most others.
Oh, and I missed the 'death cap' - What was that ?
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- Feb 12, 2006
- 60,963
- 5
- 220,655
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
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The other Garnet schematic which I posted in post #578 has only one pair of EL34s, but that wasn't the one to which AE1 was referring.
Lots going on here, all in one thread.
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And a cathode resistor biased output stage to boot.
Sounds like the fellow at Garnet had a copy of that book in his personal library.
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I think pretty much everybody designing tube amps at that time had a copy of that book.. . . Sounds like the fellow at Garnet had a copy of that book in his personal library.
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- Feb 12, 2006
- 60,963
- 5
- 220,655
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Many of the guys came out of military and commercial experience and were wary of coloring outside the lines too much. Those that did color outside the lines made some terrible amps, horribly unreliable. Not all of them but there are many that lost family fortunes in the quest of amp manufacture.
death cap, failure of the hum reducing cap on the 117 line give chassis 117v ac. There are ways to eliminate the cap.
The Radiotron Designers Handbook 4th edition was a joint venture between RCA (USA) and AWA (Australia)
I have a first edition in my library - has about 30 pages
IMHO the third edition is more theoretically focused but for me is easier to read and understand
In those early days of radio and audio engineering, spurred on by two world wars, the research was intensive as engineers strived to develop new and better ways of producing apparatus that was useful to mankind
Today's engineering is just as intense - and with many more players in the game - with a different focus, but still building upon that early work
But as always, the end product is limited to the components and devices available at the time
As an example of progress, the Sanyo STK series integrated power amplifier circuits have been around for a very long time - maybe 40 years. This one was released in 2003 and features Class D operation Sanyo Electric presents miniature D class amplifier
A more modern (2009) IC is the TDA8953, which delivers up to 420 watts (PMPO) into 8 ohms - https://www.nxp.com/docs/en/data-sheet/TDA8953.pdf
Put a bass preamp in front to it and you have a low cost bass amp.
In times to come, when the preamp becomes integrated into a single chip, a bass amp will comprise a preamp chip, a power amp chip and a SMPS chip - housed in a small moulded plastic case
The future career prospects for bass amp designers and service techs look bleak
People might then moan about the loss of point to point wiring, tubes and tube sockets and repairable amps
It's called "progress"
