JTM45 grid resistors ?

[worth]

Looking at pictures of original and Germino JTM45s' .... it seems there are no grid resistors on pin 5 of the output tubes. Am I seeing this correctly ? Most of the pics aren't very sharp.

[HotBluePlates]

Both of those are modern builds, even if well-executed modern builds.

I don't see a grid stopper either. It's not necessarily needed, but when it is needed, it sucks to have to chase the cause of oscillation and un-do your pretty wiring to add a grid stopper. I normally include them "just because".

The oldest Fenders didn't use grid stoppers either. Often not even screen resistors. That may or may not be a good thing in an amp that's getting cranked, and may have tubes of questionable quality installed (mainly thinking about screen resistors here). Those 2 cases result in 2 different reasons for possibly needing screen resistors. But I guess all that is moot since the JTM45's in quesiton both have screen resistors (although they look to be 470Ω, implying the use of KT66's or 6L6GC's rather than EL34's).

[worth]

I wonder why Ceriatone uses such a large value grid resistor , when the original JTM45 had none at all. Maybe , because the Ceriatones are sold as kits... and novice builders may have really sloppy lead-dress ?

[sluckey]

I wonder why Ceriatone uses such a large value grid resistor , when the original JTM45 had none at all.

The orig JTM45 is a bootleg Fender 5F6A and the Fender did not use grid stoppers. However, by the '60s Fender and Marshall were using grid stoppers because it's a good idea. If they were still building those amps I bet they would be using grid stoppers.

[stratele52]

I wonder why Ceriatone uses such a large value grid resistor , when the original JTM45 had none at all.

The orig JTM45 is a bootleg Fender 5F6A and the Fender did not use grid stoppers. However, by the '60s Fender and Marshall were using grid stoppers because it's a good idea. If they were still building those amps I bet they would be using grid stoppers.

+1

What is those "big" resistor on outputs tubes's socket if not gridd stopper resitor ?

[DummyLoad]

What is those "big" resistor on outputs tubes's socket if not gridd stopper resitor ?

screen current limiting resistors.

--DL

[HotBluePlates]

I wonder why Ceriatone uses such a large value grid resistor , when the original JTM45 had none at all.

Because they're using the 5.6kΩ grid stoppers that eventually showed up in later Marshall amps.

If you're producing these things, it's easy to overlook some detail that a buyer might think is critical. When I made Hoffman board kits, I overlooked at first the different power supply dropping resistors for different variations of the AB763 circuit.

A different time, someone bought a 5F6A board from me and had me install it in their amp. I knew that the 250pF, 0.022uF, 0.022uF was different from other Fender tone stacks, but did not know at the time that Fender used 3 different variations in stock 5F6-A Bassman amps. Turns out the 250pF, 0.02uF, 0.1uF variation was actually the most common in spite of what the schematic says (at least, according this this customer who I'd credit as being well-informed). Anyway, the guy was livid I didn't use the values that aren't on the schematic...

I get the impression Ceriatone (and many kit suppliers) are attempting to help DIY folks complete a credible build easily. I think few kit companies are going to extremes to help you build a "forgery" exact in every detail.

[stratele52]

What is those "big" resistor on outputs tubes's socket if not gridd stopper resitor ?

screen current limiting resistors.

--DL

+1