Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: daveyajd on July 02, 2019, 10:50:49 pm

Title: Metal Can 6L6
Post by: daveyajd on July 02, 2019, 10:50:49 pm

I happened upon these in my favorite surplus equipment and parts store. I don't have a tube tester to check them out so I popped them in one of my TOS style builds and they work great. I just got to wondering how these handle plate voltage and if there is anything I should be aware of before I put them to good use in one of my amps. What is a safe plate voltage for these older 6L6s?


Aaron

Title: Re: Metal Can 6L6
Post by: tubeswell on July 02, 2019, 11:23:37 pm

In a metal* case tube, Pin 1 is connected directly to the metal envelope and should be grounded. (so don't try and use Pin 1 for a screen resistor or grid resistor anchor point).


https://frank.pocnet.net/sheets/021/6/6L6.pdf (https://frank.pocnet.net/sheets/021/6/6L6.pdf)


https://frank.pocnet.net/sheets/121/6/6L6.pdf (https://frank.pocnet.net/sheets/121/6/6L6.pdf)


https://frank.pocnet.net/sheets/127/6/6L6G.pdf (https://frank.pocnet.net/sheets/127/6/6L6G.pdf)


(*whereas in a glass tube, Pin1 has no connection)

Title: Re: Metal Can 6L6
Post by: 2ndserve on July 03, 2019, 07:15:07 am

Design max Plate Voltage standards are substantially lower on a 6L6 compared to a 6L6GC. In Class A operation, 360V and 500V respectively. It's rare to find a commercially designed guitar amp that will allow for 6L6 use where GC's are called for.

Title: Re: Metal Can 6L6
Post by: daveyajd on July 03, 2019, 04:39:44 pm

Thank you for all the info. I can’t remember exactly what the plate voltage is in the TOS I tried them in. It seems like it was between 350 and 400 volts. I will also keep in mind not using pin 1 in any amps I may use them in.


Aaron

Title: Re: Metal Can 6L6
Post by: DummyLoad on July 04, 2019, 10:24:47 am

the 6L6 metal can tubes are rated at 19W of plate dissipation, the 5881/6L6GB are 21-23W (depends on mfg. claims) and the 6L6GC is 35W. being a metal can, you won't be able to tell if they are red-plating in your amp. best to save those for old radio restorations were designed to use them. just my 2cents.   

check plate dissipation when installed in your amp. assuming you're cathode (auto) bais: measure plate to cathode V and cathode to ground V. if you are fixed bias, then hopefully you installed 1Ω resistors under the cathodes for that. if not, you'll need a bias checker of some sort.

--pete




--pete