Why Does The Output Tube On My Vibro Champ Not Stay Lit?

[Jeffblue]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

Thanks Darg. What value cathode resistor will I need to continue running a 5881? My wife gave me the OK to purchase an Allen upgrade vibro champ power transformer. The original had been way too hot to the touch and smelled of near breakdown. I prefer 5881 over 6V6s. I'm after a really nice tone machine and I think I'm almost there.

 

[Darg1911]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

Thanks Darg. What value cathode resistor will I need to continue running a 5881? My wife gave me the OK to purchase an Allen upgrade vibro champ power transformer. The original had been way too hot to the touch and smelled of near breakdown. I prefer 5881 over 6V6s. I'm after a really nice tone machine and I think I'm almost there.

I don't know. You'd have to run some numbers into that Weber bias calculator. I think max plate dissipation for a 5881 is 25 or 30 watts so I guess you could get around 10 watts or so if everything was optimal and your OT was up to the task. You should really read up on that tube in a SE amp. A lot depends on the plate voltage and the OT primary impedance and also what you want from the tube/amp. There is a bunch of stuff about load lines and linear operation that is beyond me. Unfortunately, I'm a follower, not an innovator when it comes to this stuff.

 

[Jeffblue]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

Thanks Darg.

 

[hamerfan]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

I use a NOS Tung Sol 5881 in my 5F1 clone. I purchased a special Hammond tranny with different outputs. So i can use the 4 ohm with the 6v6 and the 8 ohm with the 5881. To bring the filiament current draw down i substituted the pilot light bulb with a led.

 

[Jeffblue]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

Gentlemen..........I installed a 490 Ohm carbon comp resistor and a 20 uf 200 volt cap and the amp sounds excellent (using the 5881) kind of like a low power twin (perhaps running a little cold) The previous resistor was reading 606 Ohms out of the circuit when all was over-heating. I'll use pedals for dirt. I feel very little warmth on both transformers and I'll try a 6V6 later to see if there is still a red plating issue. I want to thank all of you who has replied and offered their help....you are a good group to hang out with here on this forum. I can only hope I can learn enough to help others as you guys do.

 

[jeremy]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

glad it seems to be running safely!

 

[Jeffblue]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

All is good.....6V6 is not red plating. I can effectively swap 6V6 to 5881 (probably not biased quite right but they both sound great)

 

[Darg1911]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

Happy to hear it's working now.

 

[Jeffblue]

Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?

I have to thank all you guys for your input, insight and sharing your experience and knowledge with me. It is always a blast to hang out with you guys on this forum. I have more confidence about working on my amps and for that I thank you. I may now have enough confidence to tackle a project that I have been unable to finish, a Mojotone Studio One.