New '65 SRRI is Much Quieter than 2003 '65 SRRI .. Why???

[old guy]

Hi folks,

Besides 15 years in age difference and all preamp tubes in the 2003 are CV4004 Mullard russians, why would there be a 25% volume difference in these same amps? Is it the preamp tubes?

The new amp has the factory set of GT 12ax7a pre tubes as well as the factory GT 6L6s biased at 38mA.
The old amp has new GT 6L6s with all pre tubes the CV4004s - with 6L6s also biased at 38mA.

Same settings on the amp controls, same Jensen OE speakers. Is it the CV4004 preamp tubes in the old amp causing this? I'd swap them out so I wouldn't haveto bug you guys but arthritis in both wrists sometimes makes me useless for awhile.
Thanks

[bob p]

Just wondering -- how did you arrive at the 25% volume difference figure? Is that a qualitative estimate, or did you actually perform a measurement? The best type of measurement, IMO, would be to sweep a signal across the amp's input and measure voltage output at the speaker terminals and dB output with a meter.

There are so many ways that two amps could be different that it's hard to offer an opinion without guessing. That said, my first guess would be tired power tubes, assuming everything else in the amp checks out. If all of the tubes have been changed, biased, etc. then it's time to start swapping speakers and tubes, and to start taking voltage measurements.

[old guy]

Hey bob p,

Just ears my friend ... just ears. Been gigging steady for 4 decades plus and know what my 'money makers' need to sound like. I bought this new 2017 back in November to be a backup for my 2003. I feel Fender has really let me down. Yeahhhh I could of and, still could, take it to a warranty station but thats' about a 70 mile round trip I can't do on a harley.

[bob p]

I understand the difficulty of getting to a far away warranty station ... but how do you get your SRRI to gigs?

[old guy]

my ride. ok thanks ... byebye

[Mick Bailey]

I'm with Bob on that it could be the output tubes - that would be my first change. Biasing only makes a small difference in output level unless it's polar extremes and even then you only see it on a scope and often makes little difference to how loud the amp sounds. Comparing two amps with the same settings on controls can be misleading and you have to scope it to see the point where each amp begins to clip and juggle the tone controls to give the best looking signal and best output. Pot tapers and values can be considerably out (+/- 20%) so when you look at the stacked tolerance through the gain and tone stages there can be a fair difference.

[pdf64]

Is this 25% discrepancy regarding gain, or sound pressure level?

...Comparing two amps with the same settings on controls can be misleading and you have to scope it to see the point where each amp begins to clip and juggle the tone controls to give the best looking signal and best output. Pot tapers and values can be considerably out (+/- 20%) so when you look at the stacked tolerance through the gain and tone stages there can be a fair difference.

Yes, pot track value tolerance is usually only 20%, 10% at best, but I've never seen a tolerance spec for 'conformance to taper'; so really the taper could be pretty much anything, and so setting both amps to '4' or whatever is indicative of nothing; they're guitar amps, not precision calibrated lab gear.
So if they're only 25% different, it seems a major win!

The only valid setting when comparing amps in this manor is to turn all amp tone / vol controls up full. Then, controlling sound level from the instrument, flip from one amp to the other with a AB pedal.
With the guitar set very quiet, what's the difference in SPL? That's the gain difference.
With the guitar set to max, what's the difference in SPL? Assuming reasonable output from the PUs, that's the difference in power output.

It's worth plugging one cab into the amp chassis of the other, as perhaps the speakers aren't the same spec, or even one may have failed.
Perhaps the older amp uses the P10R, whilst the later has the newer P10R-F? https://www.jensentone.com/vintage-alnico/p10r-f

Hope the arthritis eases up soon

[bob p]

I think it'd be a lot easier (more objective and less subjective) to inject a sine wave at the input and measure voltage into a dummy load, and if necessary, trace voltages through the amps.

The variance could be anywhere or everywhere, so everything else amounts to taking blind stabs inthe dark.

It's interesting that the P10-Rf has lower sensitivity than the P10-R.

[big_teee]

What about plate voltage.
I've found High HT= Loud!
At least it did on my 2204s with different PTs.
Check the voltage of each, and see which one is highest?

[nosaj]

Hi folks,

Besides 15 years in age difference and all preamp tubes in the 2003 are CV4004 Mullard russians, why would there be a 25% volume difference in these same amps? Is it the preamp tubes?

The new amp has the factory set of GT 12ax7a pre tubes as well as the factory GT 6L6s biased at 38mA.
The old amp has new GT 6L6s with all pre tubes the CV4004s - with 6L6s also biased at 38mA.

Same settings on the amp controls, same Jensen OE speakers. Is it the CV4004 preamp tubes in the old amp causing this? I'd swap them out so I wouldn't haveto bug you guys but arthritis in both wrists sometimes makes me useless for awhile.
Thanks

Since you have 2 amps. Label the tubes in the positions they are in. and swap them into the other amplifier. This will tell you tubes or not. Simple enough to do without any tools.
BTW what part of Fl are you in? There are 2 of us in NWFL pensacola area and one down South somewhere.

nosaj

nosaj

[g1]

I'm not sure if you meant full clean power, but you did state that all the controls were set the same.
In that case, how much extra do you have to turn up the volume on the new one to sound the same loudness?
In any case, yes, preamp tubes can differ in gain. Sovtek actually has A,B, and C suffix's to denote this difference. But you should be able to work around this by adjusting the volume control, and full power should be about the same.

[The Dude]

My experience is that those Fender/GT preamp tubes sometimes have one of the triodes dead or at least very low gain. I like nosaj's idea about swapping tubes. You might even try them one at a time to see if there's just one bad one.