Cornford Roadhouse pre-amp tubes.

[richard]

Had a microphonic pre-amp valve in my Roadhouse so decided to replace all three. After a chat with Hotrox I decided to give the JJ Gold Pins a try. Others have described them as being smooth sounding and I would agree with that description. They add a nice warmth and punch to the un-boosted sound. However, when I kick in the boost the amp just doesn't cut like it did before. Played my first gig with the new tubes the other night and a friend who comes to lots of my gigs said he couldn't hear me very well. Reminds me of a Boogie I played years ago - lots of singing sustain but no balls.

I'm inclined to put my two working original tubes in V1 and V2 and leave the JJ in the phase splitter slot.

Anyone have any thoughts ?

Cheers All, Richie.

[BigB]

I'm inclined to put my two working original tubes in V1 and V2 and leave the JJ in the phase splitter slot.

First thing to know is that a 12AX7 (well, 12A<whatever>7) are dual triodes, that is 2 triodes (2 gain stages) in one bottle, so you really have V1A, V1B, V2A and V2B (and eventually V3A if the amp uses a cathodyne PI).

Usually V1A (first triode of V1) is the very first gain stage, which has the more influence on your overall tone and is the most subject to microphonics issues - obviously since everything else will amplify what this stage produces. What V1B and V2 are used for really depends on the amp, and V3 is most often the PI (if a long tail pair is used) or a last gain stage + a cathodine PI (typically the Peaveay Classic 30).

Now I don't have the Roadhouse schematics at hand and google was not my friend, but unless it has a tube-buffered loop, chances are that the boost part comes from either V2A or V2B but it might come from V1B too, cannot tell :-/

Anyway: odds are that your microphonic preamp tube was V1, so putting it back might not be a solution - but that's easy to check out. You could also try your old V2 in V1. Or even swap your new tubes positions and see if it makes a difference, which would not be such a surprise given the very wide tolerance wrt/ specs on current tubes.

Ok, not really an helpful anwser, but without the schematics it's really a wild guess game  :?

[Dmoney]

I'm inclined to put my two working original tubes in V1 and V2 and leave the JJ in the phase splitter slot.

Anyone have any thoughts ?

It's safe to say you can try it without damaging anything so you may as well give it a go. Just do one at a time, stop, play... you know. If you find one of your old valves works better in a certain spot then there you go, problem solved or at least you've made headway. 

Not all 12AX7's are equal, if you look through the glass you can probably pick out differences in construction. The gold pin JJ's for me aren't worth double the cost of the normal ECC83S. Their construction is pretty much identical and they don't sound that much better/different. A better valve to try out would be the larger plate (the big grey panels inside the valve) JJ ECC803S. Which is £11 at Hotrox.

The JJ ECC83S (gold pin or not) however is a very rugged valve and less prone to going microphonic prematurely.

[gwEm]

The JJ ECC83S (gold pin or not) however is a very rugged valve and less prone to going microphonic prematurely.

true dat. JJ sound totally ok and are a good balance of tone, reliability, cost and gain. I got a bunch of NOS valves and prefer a JJ in certain positions still.

Nevertheless, the phase inverter is (for me) quite an important valve tonewise. It depends on the amp clearly, but you might find NOS valves in V1 and the phase inverter and JJ elsewhere gives a good result. Thats what I do anyway ;)

[richard]

I've now done two gigs and two rehearsals since installing the JJs and I could swear the tone is improving. It's at least partly due to re-thinking the eq and gain settings but I'm sure the basic tone is getting better.

I'll be able to evaluate this a little more at Friday's gig because it's a bar I've played in countless times and I know what the room sounds like. I know it takes a while for power tubes to break in but I've never given the same consideration to pre-amp tubes.

Anyone have any thoughts about this ?

[BigB]

I've now done two gigs and two rehearsals since installing the JJs and I could swear the tone is improving. It's at least partly due to re-thinking the eq and gain settings but I'm sure the basic tone is getting better.

I'll be able to evaluate this a little more at Friday's gig because it's a bar I've played in countless times and I know what the room sounds like. I know it takes a while for power tubes to break in but I've never given the same consideration to pre-amp tubes.

Anyone have any thoughts about this ?

As far as I know each an every tube will drift a bit during the first hours (well, during it all lifetime in fact, but _speciailly_ during the first - and last - hours). But I think it's first and foremost your hears and brain getting used to the new tubes and settings.

[HTH AMPS]

Playing with the EQ would be my first suggestion.

I'd also note that of the two JJ ECC803s I've had here, both were too microphonic for the first gain stage of an amp and had to be used in the V2 spot.

[jpfamps]

I prefer the sound of the ECC803s to the ECC83s, and we started using these in our heads.

I have to admit I was concerned about microphonics when we started building combination amps, but to date I've only had one ECC803s become unusably microphonic, and that was in a head. In fact we've had far more problems with power valves becoming microphonic/ rattley in both heads and combos.

Having said this, our amps aren't massively high gain; the high gain combo is the worst environment for valves.

Thus, I don't recommend the ECC803s in high gain combos.

[richard]

Did another gig and a guitarist friend of mine whose judgement I trust said I had a great sound. I think it may be down to my loss of hearing in the top end range after hundreds of loud gigs.