Vintage amps and tube removal.

[nanchangbob]

I spent the day at a friend's home that and he has more than 10 vintage tube amps. Many of the amps have a tuner section in them and he no longer listens to the radio. He mentioned that he hates seeing the tuner section tubes go bad when he doesn't even use them.

I asked him why he doesn't just pull the tuner section tube out? He said that he was told that it would not be good for the amp as it would change the load on the transformers and change the operating points. I would think that these small signal tubes would not draw much current anyway and it shouldn't cause any problems, but I would appreciate some thoughts from those of you that have more knowledge with these vintage amps. Some of the amps he has - Fisher, Magnavox, Marantz, Dynaco, McIntosh.

Thanks,

 

[rayma]

he hates seeing the tuner section tubes go bad when he doesn't even use them.

Leave the tubes in, since the unit is designed for them to be operational.
Unregulated power supplies are sensitive to loading.

 

[huggygood]

raising tubes means MORE than B +, so you have to reset the output stage and / or the operating point of the others

 

[mozz]

You are not going to raise the b+ much of anything by removing the tuner tubes. The filament voltage for the remaining tubes will go up, that's what i'd be worried about.

 

[rayma]

Lightening the filament load on the transformer will indeed raise the HV, as well as the filament voltage.

 

[JMFahey]

Ok, so he does not use the tuner section today.
In 10 years those tubes will be more "worn" than today ... so what?
It is even less likely that he will listen to FM or AM 10 years from now so why worry?
Pulling them is a non solution to a non problem.

 

[huggygood]

 

[nanchangbob]

He has some nice tubes sitting in the tuner sections that can also be used in other parts of his amps 12ax7, 12au7 and other common tubes that he can use in the future in the gain stages. I guess he could just pick up some cheap tubes and just stick them in the sockets and save his Telefunken, Amperex and other nice tubes he has.

So it is an issue if he wants to save some of the expensive NOS tubes that are not being used, as I said he has a lot of amps, 10-20 amps.

thanks for you thoughts,

 

[trobbins]

I'm with JMF, as I'm guessing he only has one of those amps on at a time?

I'd also be surprised if any tuner section had even one 12AX7 or 12AU7 in it, let alone more than one - was that a cursory remark, or did you check in detail?

I doubt the B+ load change would really be of any concern, except for the operating B+ of other preamp stages that may need tuner section current to pull their B+ down to a designed operating level due to series RC droppers in the B+ distribution.

I doubt heater voltage change would also be of any concern unless the modern mains AC voltage was causing the heater voltage to be over +5% tolerance for starters.

 

[6A3sUMMER]

Most vintage amplifiers were rated for 110V, 115V or 117VAC. Have your friend take a look at the tags on all his amps.

A lot of todays wall power is 120V nominal (I get 121 to 123VAC on a True RMS DMM). Have your friend take a look at his wall power voltage.

While your friend is checking voltages, he might check the B+ voltages, and if they are just a little high, he might think about how much longer a used/aged/vintage electrolytic will withstand the extra stress.

The filaments are already probably getting near to, or more than their rated voltage. Removing some tubes will only make the situation worse.

Then have your friend decide what to do about the higher wall outlet voltage.

A 12AX7 or 12AU7 might be used in the Multiplex or Audio section of the tuner. They will not be in the RF Amp, Oscillator, Mixer, or IF sections of the FM tuner. The RF Amp, Oscillator, Mixer of the FM tuner will likely be 'RF' triodes, or a multi-grid tube for a single tube Oscillator/Mixer. The IF/Limiter stages of the FM tuner will likely be Pentodes.

 

[JMFahey]

He has some nice tubes sitting in the tuner sections that can also be used in other parts of his amps 12ax7, 12au7 and other common tubes that he can use in the future in the gain stages.

With due respect, I very much doubt that.
I expect RF tubes in a tuner, not Audio ones.
Specially NO 12AX7, very poor RF performance.

IF we were talking a Black and White TV set, we might find a 12AT7 , only dual purpose tube I know which is equally popular at RF (VHF to be precise) and Audio duty.
You might find a 12AU7 doing some kind of multivibrator duty , again in an OLD BW TV set.

But on an AM/FM tuner? ... highly unlikely .

And as said above, if the Tuner is OFF ... no wear.

 

[AquaTarkus]

He has some nice tubes sitting in the tuner sections that can also be used in other parts of his amps 12ax7, 12au7 and other common tubes that he can use in the future in the gain stages. I guess he could just pick up some cheap tubes and just stick them in the sockets and save his Telefunken, Amperex and other nice tubes he has.

So it is an issue if he wants to save some of the expensive NOS tubes that are not being used, as I said he has a lot of amps, 10-20 amps.

thanks for you thoughts,

What do you define as OFF? Is it just disconnected from the main amplifier input? If so it might as well still be ON. Or has the tuner HT been switched off, with the heaters still powered? If so, that will damage the tube cathodes.

I say, pull 'em out and rebias the power stages. It's good practice to periodically check power stage bias anyway.

 

[HarryY]

A option would be to replace the tubes in the tuner section with cheap ones and keep the good ones safely packed away.

It depends on the value of the tubes.

 

[JMFahey]

What do you define as OFF? Is it just disconnected from the main amplifier input? If so it might as well still be ON. Or has the tuner HT been switched off, with the heaters still powered? If so, that will damage the tube cathodes.

I say, pull 'em out and rebias the power stages. It's good practice to periodically check power stage bias anyway.

Tuner OFF because the whole receiver it´s part of is OFF.
OP mentioned owner has, what? 10 such receivers?

A comment was made that he would use one at a time, so only one would be ON at any time, all 9 others OFF and so not wearing.

All this is massive overthinking, for no practical reason.

 

[JMFahey]

A option would be to replace the tubes in the tuner section
with cheap ones and keep the good ones safely packed away.

It depends on the value of the tubes.

Let´s put it this way: I doubt they are worth a Million Dollars each and wear in, say, 100 hours

Very much doubt they are MUCH sought after and VERY expensive, specially in the future.

I for one would not base my Retirement plans in holding a few old Radio tubes in NOS condition.

What is the current Market Price for an old tube AM/FM tuner?
What is the size of the Market for them?

I wouldn´t lose sleep on their possible "devaluation" , if any at all.

And looking for replacements to be able to "save the "good ones" may become expensive .... somebody desperately looking for them will rise price, and create a market where previously there was none.

REALITY CHECK:

he no longer listens to the radio

 

[stocktrader200]

Leave them in. they may be worth a few dollars at most as silicon performs much better for tuning radio. If they are expensive nos audio tube types then replace them with a new cheap JJ tube or similar.

 

[jazztubes]

Dynaco FM 3 as an example

For fun's sake, here is the tube compliment in a Dynaco FM3 receiver. As you would expect, the "interesting" tubes (12AX7s) are serving as amplifiers in the output stage, or as a noise limiting discriminator pre the audio out. Depending on the design of combined tuner/amps the audio out of the receiver section may very well not contain any amplification and rely on the units preamp.

6AQ8/ECC85V; 6Al8AV; 6BA6V; 6BA6V; 6AU6/EF94V' 6AU6/EF94V; 12AX7/ECC83V; EMM801V; 6V4/EZ80V; 6BL8/ECF80; 12AX7/ECC8

IMHO I'd yank the 12AX7s, put in some JJs and sell the good ones

d