Motorboating on EL84 Amp

[The New Steve H]

Wondering if twiddling with the preamp voltages will warm it up. It's great amp, but I am not ready to say it can't be improved.

[cbass]

I've got a good joke about motorboating but I don't want you guys and gal to think anyless of me

[Reeltarded]

impossible

go ahead

[cbass]

Not really a joke per say but more like a story bout motorboatin

[Leo_Gnardo]

Wondering if twiddling with the preamp voltages will warm it up. It's great amp, but I am not ready to say it can't be improved.

Twiddle 'em down if anything. What speaker(s) you using? For warm 12's I like Eminence Texas Heat for cheap, and Tone Tubby Green for more 'spensive. I haven't heard the Eminence hemp cones yet but I bet they're - - - - mellow, dude!

[The New Steve H]

The cabinet is a 1x12 with a 12" Veteran 30 from Guitar Speaker Warehouse.

Oh, man. I just realized that's a 16-ohm speaker. They sent it by mistake, and it was too late to return it. I was going to put it in a cab I made for my church, but I had to substitute the only 8-ohm I have. I should go back and try the amp on the 16-ohm jack.

[The New Steve H]

If anyone cares, I stuck a 22 uF cap where the 8 uF job feeding the preamp used to be, and it killed the motorboating. The amp sounds great, but I am still wondering if I can make it warmer. Been reading Merlin Blencowe's stuff about changing the voltages on the cathode follower to get soft clipping.

[Tillydog]

Good news on the motorboating

I think the problem you'll have trying to get some colour into the preamp is that the EL84s take so little to drive them compared to the original 5881s. The PI will swing about 100V P-P to get full power out of the 5881s, but the EL84s only need ~20V P-P - the preamp won't have a chance to break into a sweat.

You could try some sort of PPIMV to match the levels back up a bit. (or put a whacking resistor where your 250R 'choke' is and really drop the PI and preamp voltages.)

[The New Steve H]

It does have a PPIMV.

The amp sounds really great now. Not sure what I did. It's very clear and detailed. The bass sounds good. It has a nice warm tone. Doesn't seem as loud as the 5F6A, but it's more than loud enough to annoy the neighbors.

I sort of set fire to the unfortunate LED circuit I stuck in there, but that can be fixed. I clipped the leads so it will not continue to burn while I run the amp.

I had an extra hole in the back of the amp, and I had read that you could change the tone by altering the resistance on the cathode follower, so I stuck a pot in there, and now I can change the sound somewhat. The resistance was 100K, and now it varies between 0 and 78K.

The headphone test made a big difference in the noise levels. I didn't know about it until people here told me. I plan to take my 5F6A apart and move the transformers around.

One thing I don't understand: when I was changing the big resistor on the power supply, a 1K got much hotter than the 250-ohm it replaced. I would have thought it would decrease the current and give off less heat, but I guess I was wrong.

[The New Steve H]

It's going to look nice. I hate to put it in a box.

[Leo_Gnardo]

If anyone cares, I stuck a 22 uF cap where the 8 uF job feeding the preamp used to be, and it killed the motorboating.

So . . . insufficient filtering it was. I thought you said you had 33's all thru. Oh well she's-a-feex now. And you know what to look out for in the future.

[The New Steve H]

Sorry. Four 33s and one 8.

[The New Steve H]

Fixed the LED circuit. No more open flames.

Turned out the noise I was hearing was just the single-coil inputs on the guitar. This thing is really quiet.

[dorrisant]

Nice

[The New Steve H]

Thanks. My guitar teacher did some video to show off the sound. If he ever gets it to me, I'm putting it on Youtube.