46 and the Tubelab SE

[w5jag]

Type 46 is a 5 pin tetrode that when triode strapped is a fine single ended DHT amplifier, as pointed out in the prior 12AT7 / 46 thread.

With a suitable base adapter, 46 and VT-63 is easily useable in the Tubelab SE. Prefabricated adapters are commonly available on Ebay.

Compared to a 45, the 46 biases differently, but the Tubelab SE has sufficient range to easily accomodate this tube. It takes a little more heater current, and has almost twice the amplification factor of a 45.

I set mine (VT-63) to about 275 volts and 20 mils. I started at about 25 mils, but decided that was a little hot, so I backed it off to 20 mils.

Although less powerful than a 45, they sound like a more powerful tube than 45, maybe because of the amplification factor.

Win W5JAG

 

[Tubelab_com]

307A / VT225 also works in triode with an adapter. I think that it makes a better 300B than a 300B does. I really need to hear them in P-P. I am working on that one.

 

[Steve Cresswell]

T
Although less powerful than a 45, they sound like a more powerful tube than 45, maybe because of the amplification factor.

Win W5JAG

Yes I've noticed that the 46, despite its lower power than the 45 is a much more solid and beefy sounding tube. Full of life but subtle at the same time.

Steve

 

[korneluk]

307A / VT225 also works in triode with an adapter. I think that it makes a better 300B than a 300B does...

From a private email exchange with Pete Millet, here are the suggested 307A/VT225 op points:

1) 5k load, and ~300V plate voltage, -30V grid bias (or the equivalent self-biased), ~40-50mA Ip. If you want more power you can push up to 350V or so at 50mA without any problems.

2) For lower output, run B+ of ~280-300 and a 680 ohm cathode resistor, with a load of about 5k.

Enjoy,

 

[Tubelab_com]

If you want more power you can push up to 350V or so at 50mA without any problems

I settled on 360 volts and 60 mA with those big blue Edcor 5K transformers. Pete ties G3 to G2 and plate, I have it grounded.

 

[w5jag]

307A / VT225 also works in triode with an adapter.

About a half dozen Ken-Rad VT-225's followed me home from Dayton, so I hope to give them a try soon, unless I'm out of 4 pin bases. I completely forgot to pick up any more of those.

Win W5JAG

 

[w5jag]

Pete ties G3 to G2 and plate, I have it grounded.

With only 4 pins to work with, I figured I would tie G3 to the cathode, like a 47, unless there is a compelling reason to do otherwise.

I'm at the lake listening to 47's in a Tubelab SE right now, so I know this confguration works OK in it.

Win W5JAG

 

[Tubelab_com]

About a half dozen Ken-Rad VT-225's followed me home from Dayton

I was at Dayton this year. I only bought 10 tubes (I really am trying to cut back). I got a 4500 VCT 150 mA transformer for $5, and a partially built power supply containing a very large 550-375-0-375-550 volt at 300 mA + several 6.3 and 5 volt windings transformer for $10 (nice cabinet too). I also got several MRI amplifier boards cheap to try as HF linear amps. I won't be back home until next weekend though.

The VT225 has a 5.5 volt filament. They seem to work fine in a Tubelab SE with 5 volts though. I was testing a pair in class AB2 P-P right before I left Florida. 30 to 35 WPC is easy but I haven't listened to them yet.

 

[w5jag]

I have also cut back on tube buying. I need to be selling.

I got the VT-225's ($6/each) and a NOS pair of GE 6BQ6GA, and some really nice Johnson ceramic Septar sockets from Fair Radio on Thursday, together with a few other odds and ends.

At the hamfest I got a chinese 5U4G and a pair of KT66 from Stan, and in the flea market I bought a pair of 5932 ($15 for the pair); a NOS 12BV7 and 12BE6 for a buck each; and three globe 47's for $60. Unless you count TV lamps, that was it for hollow state. I did restock on caps, building hardware, and some other small parts.

I was loaded down like a pack mule with tubes last year.

I think the crowd was up this year.

Win W5JAG