My First Breadboarded Amp

[Pdavis68]

Enzo, if I put the old one back in it is better. But I replaced a 6BQ5 (12W max plate dissipation) with an EL844 (9W max plate dissipation). My understanding is you can swap out and EL84 with an EL844 without any circuit changes and you simply get a lower wattage amp.

The 6BQ5 is an old tube. The EL844 is a brand new tube with under an hour of play time. I can try the other EL844 I have, but my guess is it's the lower wattage and not something particularly wrong with that one tube. I'll try several different tubes tonight. I have several 6BQ5s and two EL844s.

Nick, the grid stopper is on the breadboard, so pretty far away from the tube socket. I'll move that to the socket since I'll want it there in the end. I think I'll go ahead and modify the PS filters to get the screen voltage down a bit.

[g1]

My understanding is you can swap out and EL84 with an EL844 without any circuit changes and you simply get a lower wattage amp.

So the tube sellers say .
You mentioned differences in plate voltage with the EL844, but nothing about the cathode voltage.
In my limited experience with them they bias up very differently. You can't compare them if they are operated under different bias conditions.

[Pdavis68]

I'll double-check that when I get home. I thought I checked and it was only a 1V or so difference (10 vs. 11, I think). I'll let you know.

[Pdavis68]

Got everything working and put together. A gut shot and a shot of it when I was doing some burn-in.

Seems to be working really well. It's punchier than I was expecting and I'm pretty happy with the tone.



The only issue I'm having (and it's not specific to this amp) is that I want to use it in my car with an inverter, but I'm getting a ton of noise.

The guitar is a Squier strat. The noise is worse with the pickup switch in 1, 3 or 5 and better in 2 and 4 (makes sense). It's MUCH worse if I'm not touching the strings.

It goes away almost completely if I have the guitar's volume at full blast but the guitar's tone knob turned all the way down. If the tone knob is all the way down and I start to turn the volume knob down, it comes back until the volume knob gets down to about 2 or 1 at which point it goes away again.

So I'm thinking that: 1> It's a guitar problem and 2> it's grounding related.

When I'm playing, the car isn't turned on, I just have the electrical system on so the inverter will have power. So it's not motor related. While I can play with the tone knob turned down, it kind of limits my tone options. Anyone have ideas for how I can get around this?

P.S. Thanks to everyone for their help on this. It's been fun to get my first build under my belt. Already getting ramped up for my second.

[g1]

I think the problem really is that the inverter puts out a lot of noisy hash.
Some of them do not put out real sine-waves so you end up needing a lot more shielding than normal.
So it's not really that the guitar is poorly shielded, just that you need better shielding than stock because of the inverter noise.

[Pdavis68]

I initially suspected the inverter (and granted, I haven't checked it with my scope to see what kind of waveform is coming out of it), but I thought that if the tone knob on the guitar was making it go away that it was probably the guitar... I guess the next thing to do would be to take a look at the inverter on my oscope and see what's going on, then. Thanks.

[Pdavis68]

Just for completeness, I'm attaching the Epiphone Valve Jr. schematic with the changes that I made.

The transformer doesn't have the voltage marked. It's 260V.