Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: playindabluz on February 05, 2025, 06:34:55 am

Title: V2 tube in blues junior conversion
Post by: playindabluz on February 05, 2025, 06:34:55 am

I completed the Hoffman blues junior conversion. this is my 16th amp build. I am running a 12AY7 in v1 and a 12AT7 in V3. Using a 5751 or 12AX7 in V2 the amp is fine. If I try a 12AY7 in V2 the amp is silent. I have tried several new and NOS 12Ay7 in V2 to no avail.  Is this normal?

Title: Re: V2 tube in blues junior conversion
Post by: acheld on February 05, 2025, 10:30:58 am

Quote

If I try a 12AY7 in V2 the amp is silent.

Not normal, but seems unlikely. I'm assuming you've got the MV up . . .

Suggest scoping the input to the MV pot.  I suspect you'll see a signal present.

My experience with that circuit suggests that you need higher mu at that position, ie either a 12AX7 or a 5751.

Title: Re: V2 tube in blues junior conversion
Post by: Latole on February 05, 2025, 12:01:06 pm

Not normal, at all 12AY7 must work .

Title: Re: V2 tube in blues junior conversion
Post by: playindabluz on February 07, 2025, 06:25:14 am

Thank you gentlemen.  Yes, the master is dimed. I don't have a scope with me at the moment. I'll check that out at work next week. But AX7 and 5751 work great!

Title: Re: V2 tube in blues junior conversion
Post by: stratomaster on February 13, 2025, 06:41:31 pm

My money is on a dead tube.

What do the plate and cathode voltages look like?