Still no break-up. 2x 5F1's.

[Chuck H]

920k would be correct. 920, as stated in your previous post would have been wrong. These details in the reports are important. If you were still measuring from the center tab, the lack of change to the resistance during rotation could indicate a fault in the pot.

Did you test the input jack resistance to ground? Or did you decide was too unlikely and too much trouble?

EDIT: Along with the input jack resistance to ground it would also be necessary to measure resistance from the input jack to the input grid pin.

[Enzo]

I measure 920 K still turned to 0 or 12. Its a cts/ relatively new too, wouldn't it be surprising if it had issues?

I can only respond to the numbers you present. You said 920 ohms, so...

Would it be surprising? maybe so. But the point I tried to make earlier was that we need to check anything we can because you looked for the obvious things way back at the start. So when you eventually figure out what the problem is, of course it will be a surprise.

And a cardinal rule in electronics: newness is not a guarantee of goodness.


Besides, I was a lot more suspicious of the shielded cable than the pot.

[Sea Chief]

Hi-

yes I forgot the K when reading the 920 from the meter. Surely it was 99% likely that I'd done so as meter shows no "K" of course, but point taken.

Im looking up dummy loads- as my 5w speaker already buzzy-distorts on the bass strings even on vol 3 if I grind into them, so I cant use this with amp turned up for testing as it will blow. I still need a 4ohm low watt 8" speaker ideally but expensive afaict.

Any info appreciated- may be a while before I can get the parts if I need to make one.

[Sea Chief]

I'm reading up on dummy loads- seemed a simple idea innitially, but more I check/ read the more complicated it is; Im either overcomplicating and reading too far out of checking the facts or it is not as simple as I first thought. (Boxes? heatsinks? 100 ohm r's? cable thickness? my head is hurting).

Can someone tell me how to make a dummy load, to replace the 4 ohm speaker, simply for the purpose of testing my amp as Enzo suggests.

Thanks, Sea Chief.

[Enzo]

The dummy load was brought up so the amp would have something to drive while you ran a test tone through it loud. A plain old resistor of the appropriate ohms and enough power rating is all you need.

All the froo-fraw discussions are about what dummy loads act more like speakers and will emulate them for tones and stuff. All that is fine when someone wants to listen to the result. All we are looking to do is have SOMETHING soak up the power the amp produces while we take readings. So a simple resistor is fine. It is just a Champ, plain old hookup wire is plenty, it won't melt your wire. Fan cooled? Again, this is a tiny amp, not a 3000 watt PA head.

[Sea Chief]

Ah good. Ok I dont have a 4Ohm resistor. Maybe a daft Q but is a 100r 10w fattie, any good? (I know a 4r fattie better but got nowt). Or a 1/2w 10r ?

[pdf64]

Neither of those would be suitable.
If you have a Maplin locally, see if they have a couple of Wirewound 10 Watt 10 Ohm Resistor | Maplin available, and arrange them in parallel.

[Sea Chief]

Neither of those would be suitable.
If you have a Maplin locally, see if they have a couple of Wirewound 10 Watt 10 Ohm Resistor | Maplin available, and arrange them in parallel.

Hi pdf64,

aha ok as I thought. Ok Maplin in nrby town (S-on-Avon) so will get on mon. Thanks, Sea Chief.

[Sea Chief]

Pdf64

got me a single 3.9 Ohm, 7w wirewound. Any good?

[eschertron]

my 5w speaker already buzzy-distorts on the bass strings even on vol 3 if I grind into them

Yes, every Champ will do this, as stock, I'm afraid. There are ways to limit the bass via the coupling caps, also the cathode bypass caps. Discussions abound on this forum. The buzzy, 'farty', distortion is a good sign that you have gain on tap. Test my hypothesis by playing a few power chords on all BUT the bass strings. then turn the amp's volume up and play again. Any fizzy guitar-type distortion there? I'm hoping so.

got me a single 3.9 Ohm, 7w wirewound. Any good?

Be careful of the heat generated, it could cook the resistor if you are really pounding it.

[Sea Chief]

No fizzy whatsoever- well not until 9.5. Its simply cant in any way be a 'correct' distortion sound escherton. It sounds like crap, like amp is plain broken tbh/ or like spkr has a split or something. Ive had enough amps in my time to know what an ill amp sound is, & this is pg1 ill amp sound! My hunch is its just a 5w hifi spkr & totally unsuitable as a gtr spkr/ just cant handle what its being fed with even on vol 3 (& it goes to 12 so thats only 1/4 on the dial).

Ok Im getting a 1/2 decent 8" 4Ohm tmrw (from a buggera 5w cheapo gtr tube amp) so this crap is going in the river. I can then at least do some better 8" testing. If that sounds similarly broke/ buzzy nasty then there's defo a prob with the circuit. Im quite sure it wont sound ill tho.

Was the idea of the 2 10r fatty 10w in parralel.. to dissipate heat then?? (I thought 2 because it was just you cant get as low as 4 Ohms in this size R). Christ this amp stuff is exhausting me.

[eschertron]

so this crap is going in the river.

...at least the fishies will be pleased!

Was the idea of the 2 10r fatty 10w in parralel.. to dissipate heat then?? (I thought 2 because it was just you cant get as low as 4 Ohms in this size R). Christ this amp stuff is exhausting me.

I think 10R is probably easier to find than 4R power resistors (or 5R, since that's what two 10s in parallel will be), but also two 10W resistors will dissipate 20W of power. You should get whatever Ohmage and power-handling capacity you think is appropriate for the task. Also (just thinking out loud), three 10R resistors in parallel would be about 3.3 Ohms, maybe a better match to a traditional Fender OT.

[Enzo]

Oh goodness... it doesn;t matter. 4 ohms 5 ohms, just anything in the ballpark is good enough, this isn;t lab work.


Power resistors come in any value you like.

[Sea Chief]

.. to a traditional Fender OT.

?! [..spits tea all over the carpet].

I thought it was the physical size thats more the important factor here Enzo, ie the heat invloved as escherton alludes to, rather than a precise 4 Ohms Im sure the OT will be ok with a ballpark '4 ohms' here ok

So is my 4ohm 7w ok then? its really quite a chubby chap, and I'll ony do a quick test each time I'd think?

[Enzo]

If it doesn;t get real hot, sure.


You said it yourself, we are just taking some measurments. This is not a 1000 watt power amp on the test bench for long term testing.

The only reason I speak of dummy loads here is in case you get tired of hearing it. I often use 100Hz instead of 1000Hz in my shop, just because it is less tiring to hear it.