New tubes vs stock tubes in Fender amps? Are the old ones that bad?

I would. It's not a definite thing that Leo Fender had "hot bias" foremost in his mind when designing amps. He was out for circuits that sounded good (at any volume) and were ultimately reliable.

Warming up the bias may certainly help, but the circuit should be able to stand on its own merit, IMO.

 

Usually Fender puts in the best tubes they can. I'm not saying their the best tubes out there but like most large companies they have contracts with venders for specific parts and some kind of quality control. As far as biasing, there is no specific bias set point. Rather there is a range where the bias is within proper specification for the amp. Changing the bias to suit your ear isn't the proper way to bias and usually pushes the bias higher because you like it's sound better. However, the Bias Pot isn't a tone control. I don't know for sure if Fender biases their amps cold or just has a factory average setting. I assume if they bias cold it's to help the tubes last longer. I know when I got my 2011 DRRI it was a tad colder than some bias charts, not as high as others. To my ear it sounded good and I didn't rebias or change any tubes. Plate Voltage and Bias are both a concern, usually I adjust the Bias to compensate for the Plate Voltage.

 

Yeah, but the B- range could be several mA or volts depending on the PV.

 

Great post ++double plus good.
I have no idea if it's true or not, no offence intended,
as I haven't a clue I likeed the way that you addressed the question.
How can amps be self biasing. I read and amp stat thingy an it was claimed
I think , one could use 6v6 or 6L6 tubes?

 

My experience on the newer Fender re-issue and Blues series of amps, they are biased on the cold side. I'm sure this is for longevity/reliability reasons. Typical I'll measure the bias at 25ma on a 6L6 and about 18ma on a 6V6 for these "newer" amps.

 

Sounds about right, but you might consider the plate voltage when you adjust the bias. Higher or lower plate voltages change the bias required for the amp to work properly. For example when I changed power tranny's in my DRRI it raised the PV to about 450V and I had to raise the B- to about 21.7mA.

 

This may be slightly off topic - but if a customer - or myself - purchased a tube amp from like - Guitar Center - and they brought the amp to me just a few weeks later stating poor sound or whatever - I always recommended a full tube replacement.

Why?

Most of the tube amps at GC are sold off of the floor - so the tubes are cycled on and off several times before they are sold - and in my opinion - short on and off cycles shorted the life of the tubes.

And we never had any issues after that.

That's my two cents - which may not matter as much as I am not in the amp repair business anymore - and I only play the amps I build. So take it for what it's worth.

 

Fender does bias their amps cold to make tubes last longer.
Most tubes Fender ships in their amps are Chinese rebranded tubes.
It is pretty well agreed that Chinese tubes aren't as good on the whole as
Russian and Czech tubes being made today.
I've heard the Chinese are gettin better, but I still don't want any.

 

Totally disagree.

Russian tubes were designed for 1000 hours service life at relatively conservative supply voltage per Soviet era data sheets. The incentive to build good tubes was an extended Gulag vacation if you didn't... kinda like livin' in Vermont this winter come to think of it.

I don't think there is any incentive to build good long lasting tubes these days.

If you've ever purchased cheap incandescent light bulbs and had 'em blow with a flash every time you turn the lights on... it's like that.


Original U.S. made tubes were designed to last 10,000 hours.

Pre- CBS Fender took advantage of the durability of what are now NOS tubes. They ran the plate voltage high and they biased 'em hot. '60s tubes still lasted for years and besides, there were half a dozen TV repair men in every little town. Every TV repair man had a caddy full of tubes and a tester. Peel off a couple bucks, you'd be good to go with the same tubes guys pay big bucks for, now.


Oddly the supply voltage in the PRRI is 440v, even higher than the 420v or so seen in original Princeton Reverbs. That's over 100 volts higher than any 6V6 data sheet recommends. The only way to make new tubes last in a stock DRRI or PRRI is to bias 'em cold.

 

Biasing can help, but no amount of biasing is going to replace switching in a really good sounding v1 or sometimes v2 in the amp.

 

+1
Good point!

I have the original RCA 6L6's I took out of my Twin Reverb after 20 years of service and saved them, they all test as good as any new Russian or any other 6L6 I've tested. I've been offered $50 a tube by a guy who builds custom amps. Think I'll keep them a little longer......

 

I have 3 RCA 7025 that I took out of my 68 sf twin and they still test good after 46 years so am using 2 of them in something else I bought recently, smaller, lighter.

Had them in storage for a few of those years so don't really know if they would have made it through the night if they had been used all that time.

 

Been a while since I bought a new Fender amp stock, but when I did it came with Fender branded Sovtek tubes, did not like. Swapped to NOS Philips EL84's (Pro Junior) and GE JAN 5751 in place of the 12AX7 in the gain stage to smooth out the gain. Liked the result.

 

I think they use groove tubes now for new amps. Not sure if they are good or bad. When they need replacing a lot of people go for JJ tubes, Again I am not sure on the quality of those.

 

Groove tubes are Russian, Chinese, or JJ's (Slovak) with Fender's GT silkscreening. The silkscreening adds cost but no value.

The DRRI that I bought a few years back had Electro-Harmonics 6L6's and everything else was Sovtek. They were all Groove Tubes.

I replaced V2 with a Mullard reissue and the 6V6's with JJ's. It worked fine for 4 years and then I sold it to "thin the herd". The buyer wanted it "all original" so I put the GT's back in. He played it, liked it, and bought it.