Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: imgumby001 on August 21, 2022, 02:38:23 pm

Title: 5881 vs 6L6GB
Post by: imgumby001 on August 21, 2022, 02:38:23 pm

Does anyone know if a transformer set up for 6l6GB’s would likely be able to supply 5881’s? I don’t have specs on the transformer, so I’m really just guessing at it’s current based on what it had been running.

Thanks all!!

NR

Title: Re: 5881 vs 6L6GB
Post by: acheld on August 21, 2022, 03:47:46 pm

They are fraternal twins -- ie, not identical, with the 5881 being a buff version of a 6L6.   Near as I can tell, any PT/OT setup that will work for one, will work for the other. 

https://frank.pocnet.net/sheets/127/6/6L6GB.pdf (https://frank.pocnet.net/sheets/127/6/6L6GB.pdf)
https://frank.pocnet.net/sheets/127/5/5881.pdf (https://frank.pocnet.net/sheets/127/5/5881.pdf)

Title: Re: 5881 vs 6L6GB
Post by: pdf64 on August 21, 2022, 04:01:21 pm

All 6L6 versions (ie that includes the 5881) have the same bogey characteristics, and are backwards compatible. ie if a circuit calls for a 6L6G, a 6L6GC (or GB or WGB / 5881) can be used.
With fixed bias circuits, of course the bias should be checked, to make sure that the idle anode current is ok.

Title: Re: 5881 vs 6L6GB
Post by: PRR on August 21, 2022, 04:41:51 pm

> are backwards compatible

Yes. Which is to say, the stock 5G6a designed for 5881 can NOT ('legally') run 6L6(m/A/B) because the screen voltage is too high for original-flavor 6L6. The 5881 and 6L6GC were new technology with tougher stuff, but *designed* to retro-replace older 6L6 applications.

That said, any '6L6' made since the 1990s is probably 6L6CG bones in old-style glass.

Title: Re: 5881 vs 6L6GB
Post by: imgumby001 on August 21, 2022, 05:01:14 pm

Thanks everyone!! I’m going to use the transformer in my build, and we’ll just have to see if all the current is there to supply everything correctly. After all, it was free, and worse case is I have to actually BUY a transformer for the amp if it doesn’t work out!

Title: Re: 5881 vs 6L6GB
Post by: pdf64 on August 21, 2022, 05:15:34 pm

What exactly are you concerned about? Are you thinking of HT or heater current being drawn from the PT?
Any 6L6 variant will draw the same heater current.
HT current is determined at idle by the bias, and at full output largely by the load, ie the OT primary impedance.
The only real difference made by one variant over another is how stressed they are by the voltage and dissipation.

Title: Re: 5881 vs 6L6GB
Post by: imgumby001 on August 21, 2022, 11:58:17 pm

Quote from: pdf64 on August 21, 2022, 05:15:34 pm

What exactly are you concerned about? Are you thinking of HT or heater current being drawn from the PT?

Any 6L6 variant will draw the same heater current.
HT current is determined at idle by the bias, and at full output largely by the load, ie the OT primary impedance.
The only real difference made by one variant over another is how stressed they are by the voltage and dissipation.

Yes. You are exactly right sir!! Thank you!!!

Title: Re: 5881 vs 6L6GB
Post by: HotBluePlates on August 22, 2022, 05:46:56 am

Quote from: imgumby001 on August 21, 2022, 02:38:23 pm

5881 vs 6L6GB

Lemme show you something:  In the old days, 5881 = 6L6WGB

Open the image in a new tab to zoom in.

(https://i.imgur.com/V25xTPq.jpg)