ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Preamp tube experiences

12/2/2003 7:39 PM
Darryl Dennis	Preamp tube experiences It seems to me that the 5e3 is really changes tone with tube changes. I am using a Hammond 272BX getting 350volts B+ with a NOS RCA JAN 5y3 and (IMHO) great power amp tone with 1953 NOS JAN Ken Rad 6V6GTs. I have found considerable changes in interaction, tone, sustain smoothness, etc. by changing preamp tubes. I currently like JAN RCA 12AY6 in both pre amp positions. I have tried several different 12ax7s ( lots of head room), 12ay7s and other various 12xx tubes. I am soliciting other opinions in preamp tube combinations to achieve a late 50s cranked amp tone…i.e. 1958 Fenton Robinson, Texas Flood, Peacock Records tone. Thanks Darryl

12/2/2003 7:39 PM

Darryl Dennis

Preamp tube experiences

It seems to me that the 5e3 is really changes tone with tube changes. I am using a Hammond 272BX getting 350volts B+ with a NOS RCA JAN 5y3 and (IMHO) great power amp tone with 1953 NOS JAN Ken Rad 6V6GTs. I have found considerable changes in interaction, tone, sustain smoothness, etc. by changing preamp tubes. I currently like JAN RCA 12AY6 in both pre amp positions. I have tried several different 12ax7s ( lots of head room), 12ay7s and other various 12xx tubes. I am soliciting other opinions in preamp tube combinations to achieve a late 50s cranked amp tone…i.e. 1958 Fenton Robinson, Texas Flood, Peacock Records tone.

Thanks
Darryl

12/2/2003 8:51 PM
Curly	I prefer good NOS tubes, and like to stick to the chart. Like any good tube amp, yes, the preamp tubes can have a big effect in this amp.

12/2/2003 9:02 PM
X-Anonymous	Hey Curly, Where's Mo? EOM

12/2/2003 9:53 PM
Darryl Dennis	Re: Preamp tube experiences Right.....What I am looking for is opinions on good combinations of tubes. I have found that two 12ay7s make a good tone on this amp setup ...I’m looking for tonal experiences with 12av7s, 12at7s, and 12au7s. I have found that 12ax7s have too much gain to allow the ken rad 6v6s to start to distort before max volume..

12/3/2003 2:55 PM
Eddie James	Darryl, I've included a great article on this which supports your position that using a lower gain preamp tube makes the tone "better". The long and the short of it is that if you consider a 12AX7 to have a gain of 100 (just to set a reference) then this article lists the following tubes and their percent of gain as compared to the 12AX7's 100: 12AX7 100% 5751 70% 12AT7 60% 12AY7 45% 12AV7 41% 12AU7 19% Apparently the lower gain preamp section, when cranked up, makes the power section work harder i.e., I think it puts the output stages in that sweet spot on the gain curve that resonates as nice tone to our ears. The article can be found at: http://thetubestore.com/gainfactor.html But here it is for quick reference: One simple tweak that is favored by guitar amp users is to plug in a pre-amp tube with a slightly different gain factor. (Important: this only works for tubes that are pinout and plate voltage compatible, such as the six types listed at right.) The gain factor of a tube simply measures how much it amplifies the input signal. For example, the common 12AX7 type has a gain factor of 100, while a 5751 (which is often used in place of a 12AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up. Many guitar amp users (particularly harmonica players) like to reduce the gain to get a different sound or calm the amp down to prevent feedback. In some cases, you can also go the other way and increase the gain factor. It is generally more risky to increase the gain factor rather than decrease it as the added gain may be too much for the rest of the amplifier circuit. An example of an acceptable up-swap can be found in Fender amps that use a 12AT7 (with a gain factor of 60) as a "reverb driver" tube. You can sub in a 5751 to increase the gain by just a touch. The tubes we list here also have several alternate names, which we list below. Note that the alternates do not have significantly different gain factors, they are simply a different name for the same thing. 12AX7 - ECC83, 7025, ECC803, E83CC, 6681 12AT7 - ECC81, 6201, 6679 12AY7 - 6072 12AV7 - 5965 12AU7 - ECC82, 5963, 5814, 6189

12/3/2003 2:55 PM

Eddie James

Darryl,

I've included a great article on this which supports your position that using a lower gain preamp tube makes the tone "better". The long and the short of it is that if you consider a 12AX7 to have a gain of 100 (just to set a reference) then this article lists the following tubes and their percent of gain as compared to the 12AX7's 100:

12AX7 100%
5751 70%
12AT7 60%
12AY7 45%
12AV7 41%
12AU7 19%

Apparently the lower gain preamp section, when cranked up, makes the power section work harder i.e., I think it puts the output stages in that sweet spot on the gain curve that resonates as nice tone to our ears.

The article can be found at: http://thetubestore.com/gainfactor.html

But here it is for quick reference:

One simple tweak that is favored by guitar amp users is to plug in a pre-amp tube with a slightly different gain factor. (Important: this only works for tubes that are pinout and plate voltage compatible, such as the six types listed at right.)

The gain factor of a tube simply measures how much it amplifies the input signal. For example, the common 12AX7 type has a gain factor of 100, while a 5751 (which is often used in place of a 12AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up. Many guitar amp users (particularly harmonica players) like to reduce the gain to get a different sound or calm the amp down to prevent feedback.

In some cases, you can also go the other way and increase the gain factor. It is generally more risky to increase the gain factor rather than decrease it as the added gain may be too much for the rest of the amplifier circuit. An example of an acceptable up-swap can be found in Fender amps that use a 12AT7 (with a gain factor of 60) as a "reverb driver" tube. You can sub in a 5751 to increase the gain by just a touch.

The tubes we list here also have several alternate names, which we list below. Note that the alternates do not have significantly different gain factors, they are simply a different name for the same thing.
12AX7 - ECC83, 7025, ECC803, E83CC, 6681
12AT7 - ECC81, 6201, 6679
12AY7 - 6072
12AV7 - 5965
12AU7 - ECC82, 5963, 5814, 6189

12/3/2003 2:51 PM
Rob Mercure	Hey Eddie, Yer mostly right but there are some assumptions in your post that might need clarification. First off the mu of a triode is dependent on specific circuit conditions and is more a theoretical gain factor than actual. Yes, 1/2 of a good RCA 12AX7 will have an amplification factor of 100 at Ep 250, Eg-2, Rp 62,500, Ip 1.2 MA - but not necessarily at 300V or 175V Ep, etc. And, since all of the tubes you mentioned did not have their amplification factor determined using the same parameters the mu is more a general guideline than a fact (and I'm not taking into account the wildly variable mu of current production tubes). As far are the lower gain tubes "making the power section work harder" - I think that you mean that for the same amplifier output more gain will have to be realized in the output section. And some of these tubes have higher plate dissipation (12AU7) and may draw more current than a 12AX7 very slightly lowering the plate supply for other preamp tubes (miniscule really). So, your overall advise is sound but the theory behind is needs some tweaking. Rob

12/3/2003 2:51 PM

Rob Mercure

Hey Eddie,

Yer mostly right but there are some assumptions in your post that might need clarification. First off the mu of a triode is dependent on specific circuit conditions and is more a theoretical gain factor than actual. Yes, 1/2 of a good RCA 12AX7 will have an amplification factor of 100 at Ep 250, Eg-2, Rp 62,500, Ip 1.2 MA - but not necessarily at 300V or 175V Ep, etc. And, since all of the tubes you mentioned did not have their amplification factor determined using the same parameters the mu is more a general guideline than a fact (and I'm not taking into account the wildly variable mu of current production tubes). As far are the lower gain tubes "making the power section work harder" - I think that you mean that for the same amplifier output more gain will have to be realized in the output section. And some of these tubes have higher plate dissipation (12AU7) and may draw more current than a 12AX7 very slightly lowering the plate supply for other preamp tubes (miniscule really).

So, your overall advise is sound but the theory behind is needs some tweaking.

Rob

12/3/2003 4:13 PM
Eddie James	Rob, Thanks for the tweak but you are fresh off the "speaker wire" thread, so I probably should step carefully or you will want to tile my toyota for me! Actually what I was trying to say is that the skin effect of tube's glass envelope is nothing to scoff at; we must all apply a shunt to the tube's exterior so that aliens won't be able to control our minds (at least our minds operating in the RF range about 10Ghz) Of course you are correct that changing plate voltage will change mu with the grid voltage constant (mu = dVp/dVg where d=delta or change so mu is the ratio of change in Ep to the change in Eg required to cause the same change in Ip). The article makes its point in the general case and I think it is valid so we can get a sense of the gain differences and how that affects tone by allowing us to drive our output sections harder at lower volumes. I wasn't aware the of wildly varying mu in production tubes. Do you mean between triode manufacturers or between a single manufacturer's production runs? Since the mu value depends on grid/anode spacing for a given type of tube, are you saying the manufacturers can't produce two in a row with their current processes? Interesting assertion you make on the mu but what is the applicability to our beloved 5E3? Eddie.

12/3/2003 4:13 PM

Eddie James

Rob,
Thanks for the tweak but you are fresh off the "speaker wire" thread, so I probably should step carefully or you will want to tile my toyota for me! Actually what I was trying to say is that the skin effect of tube's glass envelope is nothing to scoff at; we must all apply a shunt to the tube's exterior so that aliens won't be able to control our minds (at least our minds operating in the RF range about 10Ghz)

Of course you are correct that changing plate voltage will change mu with the grid voltage constant (mu = dVp/dVg where d=delta or change so mu is the ratio of change in Ep to the change in Eg required to cause the same change in Ip). The article makes its point in the general case and I think it is valid so we can get a sense of the gain differences and how that affects tone by allowing us to drive our output sections harder at lower volumes.

I wasn't aware the of wildly varying mu in production tubes. Do you mean between triode manufacturers or between a single manufacturer's production runs? Since the mu value depends on grid/anode spacing for a given type of tube, are you saying the manufacturers can't produce two in a row with their current processes?

Interesting assertion you make on the mu but what is the applicability to our beloved 5E3?

Eddie.

Page 1 of 3

Next>

Last Page>>