Fuse Blows When I Max The OD Pot

[flcmcya]

Am Pretty close to this .....need a 150 k for the FET resistor yet.

I'll try and do better with the pics.

[glasman]

Lack of shielded cabinet on the OD level control (blue wire). It is running back across all of the tone stack wires. No shielded cable on either Drive or level control potentiometers (top pot connection).

This could add to the problems.

Gary

[flcmcya]

Thanks Gary ....I could't do much better on the pics unless there is someting in particular I should be aiming at......the sheilded wires all appear to be single end grounded....and I should be adding shielded to these other locations as well ?
Is there a particular part # for the correct shielded wire as I dont know where to get it locally.

I can try to move the blue wire if it would help at all........Maybe a spot of silicone.


And many thanks and Happy Holidays as well.

[glasman]

Here is how I would do the OD level and Drive pots.

This is from an overdrive deluxe.

Gary

[bluesfendermanblues]

Glasman, Thanks for thorough explanation.

Do you always/rutinely check amps with the scope, even if they sound good?

Yes, every amp is on the scope anytime it is connected to the dummy load.

I use the following test equipment and why. Every amp goes through the same testing.

1- Scope - watch for parasitics, check supplies for supply ripple and checking cap polarization.
2 - DMM - measure all DC voltage and measure AC on speaker to tewst output power into dummy load, sorting resistors and pots.
3 - Spectrum analyzer - Test each stage for proper frequency response, gain setting and creating amp log files.
4 - LCR Meter - Measuring all signal caps for tolerance and dissipation, filter caps for value and ESR, measuring the inductance, resistance and turns ratio of transformers and chokes.

wow, that the difference between a DIY'er like myself and a PRO!

Thanks for the info. Together with Funk's and Heisthl's step-by-step lists, your above list must be the complete 'how to' build a great amp. Thanks

[flcmcya]

I did try to isolate the blue wires as everything was all bunched together.....I will hunt down some shielded wire.....thanks

[flcmcya]

I also noted my tubes are cherry red even though they are biased around 34 ma.....somethings amiss.....my soldano's are nice blue with a tint of red.

[paulster]

I also noted my tubes are cherry red even though they are biased around 34 ma.....somethings amiss.....my soldano's are nice blue with a tint of red.

That also suggests parasitic oscillation since it can mean the amp is working absolutely flat out at frequencies well above what you can hear. Red plating at a sensible static bias point is often a tell-tale sign of this.

[Structo]

Just a note of soldering to the backs of the pots.
If your chassis is powder coated like all of the D'Lite chassis I am aware of, it's very possible that the pot is not grounding well to the chassis by the mounting hardware.
I was going to solder my shields to the Level and Drive pots but when I measured for continuity one of the pots didn't register to ground.
So instead of taking those pots out and grinding the paint off, I just soldered the shields to the ground buss.

I know the shield to the back is a good way and approved by HAD, I just couldn't bring myself to tear it all apart to ground the pot.

flcmcya,
By the way, you can buy good 18ga or 20ga Teflon shielded cable from Apex Jr.
This is the good silver plated type that won't melt when you solder it.
But remember that he has a $20 minimum purchase.
http://www.apexjr.com/wire.html

So what I did is I figured I would always need more wire so I bought 15ft of just about all the colors, the shielded cable and the heat shrink kit which is a bargain I think at $8.95.

[flcmcya]

I will dig into that one tomorrow Tom.
Snowblower is whooping me right now as I have about a foot and a half to contend with.

Merry Xmas

[Structo]

Oh and just so you know.
It is recommended to use shielded cable on the Level and Drive pots.
So four runs of that.

I also use a shielded run on the master pot from the middle lug to the relay board.
But I think most use single wire on the Master.

[flcmcya]

Thanks Tom ......I checked on that but looks like they are out right now....
I'll do some snoopin!

[flcmcya]

WForgot something.....when I did the OD entrance I unhooked one side of the jumper and left it hanging under the board........could this be giving me some of that classic parasitic oscillation?

[butwhatif]

what jumper is that?

[flcmcya]

OD entrance mod.....you move the 220k resistor and replace with a .05uf cap but you remove the jumper underneath where you put the resistor.....I just unhooked one side and shrinked it in case I wanted to go back stock.