What makes an All Tube amp ?

[zzmoore]

Re: What makes an All Tube amp ?

zzmoore ... that's my understanding of what diodes do as well, in this type of application. They clip the top of the waveform which results in a type of distortion but they add no gain. I think they actually reduce gain because of their effect on the signal. They may be there because the manufacturer didn't want to add pre-amp gain with tubes. But, I think I clearly stated that they are not necessarily used for that purpose. Again, they are not a gain stage. I am no tube amp designer and I fully admit that I can struggle with a schematic. But I do know that they may also be used to voice an amplifier for a certain sound (distortion).

It's rare for diodes to be used to generate clipping in guitar applications without some kind of signal booster. Otherwise when you turn the distortion up you end up with a quieter signal. I'm assuming that when you crank a JCM800 with diodes in the preamp you don't end up with a quieter signal? If so, then I think we can safely assume that the diodes used for clipping are part of a gain circuit.

I have no education in this stuff, but I would say you two are correct.
If there is any gain associated with diode clipping, it is due to gain being added to the circuit. Either another (or hotter biased) tube is switched into the chain, or there are SS Devices attached to the diode clipping. By themselves, diodes are lossy and would reduce gain.
Some of these guys that have these amps may know, from looking at the schem, what is really going on.
I have never, really, dealt with diodes in this situation before.

[Steppin' Wolfe]

Re: What makes an All Tube amp ?

IMho, anytime the signal is processed in anything other than a tube, the amp is not an all-tube amp. Rectifiers do not process signal....they provide the power supply.
distortion created with diodes inserts soem solid state device into the signal chain. So does overdrive with IC's....as in say a JCM 900 HI-gain Dual Reverb....which also has solid state reverb, which quailifies as non-tube processing imho.

As to letting a manufacturer play with definitions in order to massage the market, that does not a tube amp make, either. EX: Fender HOT rod/Blues series, Peavey Classic 30 & 50, almost all modern Marshalls....there is solid state processing gong on in those amps...reverb for sure in the Fenders and Peaveys mentioned....and even more in a lot of Marshalls. I opened up a Vintage Modern a month ago.....solid state processing galore.....very inexpensively built amp for the money that people pay for them. I would take a 5150/6505 Peavey any day if I were looking for that type of amp...hi gain.

[Edgecrusher]

Re: What makes an All Tube amp ?

I have no education in this stuff, but I would say you two are correct.
If there is any gain associated with diode clipping, it is due to gain being added to the circuit. Either another (or hotter biased) tube is switched into the chain, or there are SS Devices attached to the diode clipping. By themselves, diodes are lossy and would reduce gain.
Some of these guys that have these amps may know, from looking at the schem, what is really going on.
I have never, really, dealt with diodes in this situation before.

It depends really on the exact amp. Some of the JCM900's the diode bridge doesnt include an IC as a gain stage and are only used for clipping. Others the gain stages are completely solid state. Some amps like the peavey ultra series have clipping diodes after the tubes. Some like in the jose arrendo mod the diodes are part of the master volume circuit. So it really all just depends.

[Edgecrusher]

Re: What makes an All Tube amp ?

I opened up a Vintage Modern a month ago.....solid state processing galore....

All the gain stages and clipping in a vintage modern is done with tubes. Sure if you open one up there are plenty of solid state components but they are for the switching and rectifying circuits. They are not in the audio path.

[Nostalgic Distortion]

Re: What makes an All Tube amp ?

Reflectors?

Stupid I pad, you know what I meant???

[Darg1911]

Re: What makes an All Tube amp ?

IMho, anytime the signal is processed in anything other than a tube, the amp is not an all-tube amp. Rectifiers do not process signal....they provide the power supply.
distortion created with diodes inserts soem solid state device into the signal chain. So does overdrive with IC's....as in say a JCM 900 HI-gain Dual Reverb....which also has solid state reverb, which quailifies as non-tube processing imho.

As to letting a manufacturer play with definitions in order to massage the market, that does not a tube amp make, either. EX: Fender HOT rod/Blues series, Peavey Classic 30 & 50, almost all modern Marshalls....there is solid state processing gong on in those amps...reverb for sure in the Fenders and Peaveys mentioned....and even more in a lot of Marshalls. I opened up a Vintage Modern a month ago.....solid state processing galore.....very inexpensively built amp for the money that people pay for them. I would take a 5150/6505 Peavey any day if I were looking for that type of amp...hi gain.

Rectifiers aren't in the signal chain but they do affect the signal, or at least they can affect the sound. Tube rectifiers drop voltage under load and don't recover immediately. "Sag". It can be heard in the output (softer attack, compression, bloom, sustain, spongier bass). I'm not arguing that it's "better" to use rectifiers (even though I am a Mesa fan and think they still have their place). Most amp designers probably don't think it is and the majority of amps are SS rectified now. But I think if were calling an amp "all tube", they get included. But again, I'm not hung up on the semantics. I don't care if it's a tube amp or an all tube amp if I like the sound.

[GuitarStv]

Re: What makes an All Tube amp ?

I don't care if it's a tube amp or an all tube amp if I like the sound.

We're probably on the same page for this one. All tube isn't a guarantee of awesome, nor is having other elements in the amp design a sign of a poor amp.