Hi,
Has anyone ever used 7058 preamp tubes? Apparently they perform similar to 12ax7's, but require a higher voltage from your PT?
I have an old NOS RCA that I wish I could sample, but obviously it is not a direct replacement for 12ax7's.
How do they compare in cost, availablity and of course "sound"?
J
7058 Preamp Tubes??
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dotfret
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Why do I end up telling the truth? This is top secret, usually ... bet the price is up next week ...
7058 is a 12AX7 variant made for car radios. Mostly, they are RCA manufactured, whatever name is on them (mostly Motorola). Sylvania made some but they are very rare.
The heaters are designed to work from a car battery, so you have to run them on the series line (12.6V connected). The centre tap is usually connected, despite what it says on the spec sheet, but if you try to use the heaters in parallel (6.3V connection), one side will die a lot quicker than the other - just don't go there!
The heaters are also designed to be flexible - they will run on the 10V that a car battery provides on a cold day, or the 14V that a well charged battery gives in a Californian summer.
Remember that a car battery has a 12V nominal voltage, but a normal and fit battery gives 13.4V under no-load conditions.
You will find they sound good on 12.6V, but give them heaters 13V and they sound better.
jgab, why don't you enable email so I can tell you and not the whole world? The forum forwards the email, you don't get spam ...
Zaphod's gonna kill me this time ...
7058 is a 12AX7 variant made for car radios. Mostly, they are RCA manufactured, whatever name is on them (mostly Motorola). Sylvania made some but they are very rare.
The heaters are designed to work from a car battery, so you have to run them on the series line (12.6V connected). The centre tap is usually connected, despite what it says on the spec sheet, but if you try to use the heaters in parallel (6.3V connection), one side will die a lot quicker than the other - just don't go there!
The heaters are also designed to be flexible - they will run on the 10V that a car battery provides on a cold day, or the 14V that a well charged battery gives in a Californian summer.
Remember that a car battery has a 12V nominal voltage, but a normal and fit battery gives 13.4V under no-load conditions.
You will find they sound good on 12.6V, but give them heaters 13V and they sound better.
jgab, why don't you enable email so I can tell you and not the whole world? The forum forwards the email, you don't get spam ...
Zaphod's gonna kill me this time ...
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zaphod_phil
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CurtissRobin
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zaphod_phil
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I'm sure you must know that in the Hitchikers Guide to the Galaxy, Zaphod has two heads and two brains 
He wasn't born that way, but just thought it would be cool to add an extra head and an extra arm (it's so much easier to solder with three). So the combined computing power of both those brains hasn't yet come up with a really good excuse to kill Dot Fret.
Anyway, I guess from what he said, you could use that 7058 tube in the V1 position of an 18W amp, and it might even sound awesome. Just you would need an extra filament transformer for the 12 to 13V heater supply.
He wasn't born that way, but just thought it would be cool to add an extra head and an extra arm (it's so much easier to solder with three). So the combined computing power of both those brains hasn't yet come up with a really good excuse to kill Dot Fret. Anyway, I guess from what he said, you could use that 7058 tube in the V1 position of an 18W amp, and it might even sound awesome. Just you would need an extra filament transformer for the 12 to 13V heater supply.
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Nature abhors a clean tube amp
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dotfret
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You guys want spelling lessons?
Check out the prices of NOS RCA 12AX7.
Compare with the prices of 7058.
Build your 18W with 12.7V heater supply on all the triodes and you can use either, without modifications. If you get a filament transformer that will deliver a little more current than usual, it makes it easy to use 12BZ7 as well.
Cmon, a set of three NOS double triodes for less than $25 if you shop around? If you're quick - the price has probably gone up $3 per valve since I made my first post.
And remember, the 7058 is an industrial spec - so tested for vibration, low noise, and long life.
I've got a large stash already, so it don't bother me.
I might mention that an old model train transformer control, coupled with a voltmeter, is useful if you want to mess about with the heater voltages.
Check out the prices of NOS RCA 12AX7.
Compare with the prices of 7058.
Build your 18W with 12.7V heater supply on all the triodes and you can use either, without modifications. If you get a filament transformer that will deliver a little more current than usual, it makes it easy to use 12BZ7 as well.
Cmon, a set of three NOS double triodes for less than $25 if you shop around? If you're quick - the price has probably gone up $3 per valve since I made my first post.
And remember, the 7058 is an industrial spec - so tested for vibration, low noise, and long life.
I've got a large stash already, so it don't bother me.
I might mention that an old model train transformer control, coupled with a voltmeter, is useful if you want to mess about with the heater voltages.
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paulschnettler
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Well, I know ebay isn't the best place to shop for tubes but....
a quick peek shows a 1/2 dozen 7058 tubes for auction with prices from $24 for a single to $98 for a matched pair of NOS.
I don't see any benefit at those prices!
What about using 7025's, any benefit to using low noise versions in 18 watters?
a quick peek shows a 1/2 dozen 7058 tubes for auction with prices from $24 for a single to $98 for a matched pair of NOS.
I don't see any benefit at those prices!
What about using 7025's, any benefit to using low noise versions in 18 watters?
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CurtissRobin
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Well, dotfret probably knows where his towel is and would thwart your attempt. Perhaps if you read him some Vogon poetry with your mike plugged into a dimed Blackface Fender just to be certain? After all, a Vogon wouldn't need an excuse.zaphod_phil wrote:I'm sure you must know that in the Hitchikers Guide to the Galaxy, Zaphod has two heads and two brains
KennyO
Who's mostly harmless and now returns you to your regularly scheduled Tube Talk Forum.
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dotfret
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You think I would quote a price on here without checking first? Any slip and the sharks rip you to shreds - so I've sent you an email - now you know the easiest place to get them, although they are a bit slow to supply, don't hold your breath!paulschnettler wrote:Well, I know ebay isn't the best place to shop for tubes but....
a quick peek shows a 1/2 dozen 7058 tubes for auction with prices from $24 for a single to $98 for a matched pair of NOS.
I don't see any benefit at those prices!
What about using 7025's, any benefit to using low noise versions in 18 watters?
These days, 7025 are too expensive because the hifi nuts pay stupid prices for them. That said, they are great in an 18watt, and Fender used to specify then in V1 for a lot of their amps.
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