Brimar 6X5GT - What uF rating

[tubeswell]

Scored an antique Brimar 6X5GT recto valve with "Made In Engand" stamped on the bakelite.

Heard conflicting stories about its uF rating. Is it 4uF, 8uF or a whopping 32uF?

Anyone know?



I want to use this tube for a Class A project. The higher uF rating the better

[stokes]

I used one in a 5E3 type clone I converted from an old PA head for someone.I put a 40uf in it and the owner hasnt had any problem in the 5 years he's had it.

[tubeswell]

Thanks for your reply Stokes

I just found these today BTW

The Brimar spec sheet (see .pdf file attached) notes 4uF reservoir condenser with a "32uF max" notation for the reservoir condenser - This is slightly puzzling to me - can anyone explain this please?

Furthermore, the "Hampshire Collection" (see link) states that the reservoir capacitor should be restricted to 16uF

http://www.r-type.org/exhib/aai0241.htm

Hmmm...

[stokes]

Most tube data you see were written for T.V. and radio applications.Even amps in those days werent meant to be pushed "over the edge" as we guitarists are so prone to do.So the "limits" were meant to give you the longest life possible.Guitar amps tend to push tubes to the limits anyway,so a lot of ratings are quite conservative compared to what we end up doing to the tube anyway.Will using a larger than recomended input cap shorten rectifier tube life?Sure,but in my experience not by a significant amount.As long as you dont see arcing in the tube when you take it out of standby and the cap gets that first surge of DC voltage,its not catostrophic.

[Steve Conner]

The 4uF is just an example value that Brimar thought would be typical of what most people would use. 32uF is the true maximum amount you can use, well according to that datasheet at least.

I'd be more concerned about the 70mA maximum current rating. You won't get a lot of power out of an amplifier running off this thing, especially in Class-A.

[tubeswell]

Thanks for your concern Steve

I was thinking to build whatever low power thing I could get away with, because the idea kind of grabs my fancy to use bits I found in an old radio to make a guitar amp - it doesn't need to be powerful - I already got a powerful tube amp.

The radio has one antique 6v6GT output tube - which has a hairline crack in the side of the bakelite. Is there some kind of modern gook I can use to patch that up with? I have an old good condition 12" alnico rola speaker I was going to chuck in.

I am searching for a simple circuit for a 12AT7 preamp, the 6v6GT and the Brimar 6X5GT - somewhere between 1W and 5W. Any suggestions/directions would be appreciated. I never built a tube amp before. (although I have modded my existing guitar amp ad-nauseum)

[Steve Conner]

Sounds like you have a kit of parts for a Fender Champ there.

As for the crack, probably best just to leave it. I can't think of any glue that wouldn't soften and smell bad when the tube gets hot.

[tubeswell]

Thanks again Steve

Checking out the Champ schematics here:

http://www.turretboards.com/schematics_library.htm

These champs all have either a 5Y3 or 5Y3GT rectifier.

I guess one look at the mains TF in the old radio will show me where to tap the Brimar recto valve, but I would feel more confident looking at a schematic for wiring a 6V recto into that circuit.

[stokes]

Just use the 6.3v heater you use for the other tubes.

[Steve Conner]

Well, if you have a second heater winding on your transformer for the 6X5, you should use it, and connect one end of the heater to the cathode. According to these guys on antiqueradios.com, 6X5s have a habit of breaking down their heater-to-cathode insulation and taking out your power transformer.

http://antiqueradios.com/forums/view...7163f2fe1d016c

Otherwise, just hook it up with all the other tubes like Stokes said.