help! my HRM overdrive sounds harsh

[Pete]

I see, I think. So, this means there would be an advantage with the switch before all filtering? At least that is how I understand it.
Just tring to clarify the disadvantage to the "switch first" method and should I change my amp. (thanks for the comments, sorry to continue the tangent)

What I was talking about there was you have the diodes with no load (no filter to set the ouput voltage) so It has the possibility of being higher than 500 volts in the initial surge. If your charging the first filter stage when power is applied this can't happen because the voltage from the PT comes up slowly (relatively) and gets to a stable point at whatever the first filter sets it to (believe it or not a filter cap sets the voltage when there's no load - try changing the capacitance on an unloaded stage, you can change the voltage drastically with varied capacitance).

[mlp-mx6]

What heisthl is suggesting is exactly how almost every blackface Fender power supply was built. The "totem pole" was pre-standby, and the center-tap plus everything else were post-standby.

One word of caution - if you do not have some type of bleeder resistor on the post-standby side then your caps will hold a charge for a MUCH longer time, possibly days. I would strongly urge you to put some sort of bleeder on the preamp end - the standard recommendation of a 150K to ground at/after the last cap as a FET-preamp substitute handles this function nicely.

[novosibir]

so how does putting a cap across the standby switch put it in parallel with the first filter cap(s)?

I haven't said, that putting a cap across the standby switch is putting it parallel to the first filter cap! Where have you read this?

Larry

[JimiB]

Sorry Larry I edited my post with this -

(nevermind on the first one it's right here)
When you have the first filter caps on the hot side of the standby switch, then I'd recommend the .02/1kV cap from the cold side of the switch to ground.

Larry

But I think you missed it. I removed it now.

[Pete]

What heisthl is suggesting is exactly how almost every blackface Fender power supply was built. The "totem pole" was pre-standby, and the center-tap plus everything else were post-standby.

I think I understand that part (I'm more familiar with BF Fender than other amps), I'm just tring to understand how it is superior to the ("standby") switch before the PS method, and why a designer very familiar with the early Fender PS would change it from typical Blackface to something like the style of #0124.

One word of caution - if you do not have some type of bleeder resistor on the post-standby side then your caps will hold a charge for a MUCH longer time, possibly days. I would strongly urge you to put some sort of bleeder on the preamp end - the standard recommendation of a 150K to ground at/after the last cap as a FET-preamp substitute handles this function nicely.

Both my 50W & 100W amps do have the FET ciruit, don't know if/how that would relate to your point but maybe this does. As a habit, I always turn off a tube amp leaving the standby switch in the "operate" position. What do ya think? Thanks

[heisthl]

What heisthl is suggesting is exactly how almost every blackface Fender power supply was built. The "totem pole" was pre-standby, and the center-tap plus everything else were post-standby.

I think I understand that part (I'm more familiar with BF Fender than other amps), I'm just tring to understand how it is superior to the ("standby") switch before the PS method, and why a designer very familiar with the early Fender PS would change it from typical Blackface to something like the style of #0124.

If you look closely at the pictures of #124 (ODS_124073) I think it is wired "correct" and the hand drawn schematic is wrong. You can clearly see the choke and OT on the SBY return and the first filter on the SBY send.

[heisthl]

The MOV should be across the wall voltage inlet. There's no benefit, to have a MOV across the standby switch.

Larry

This would make for a pretty good welder imitation - get the MOV on the other side of the amp fuse (like across the OT primary) so the fuse blows when the MOV shorts.

[novosibir]

Shure I've meant after the fuse and power switch (but in my hectic quick reply not written so)

Otherwise the MOV would control the house wiring until to its house fuse.

But yes - of course you're right and my post leads to misunderstanding

Larry

[Ears]

A question for Larry, also asked by JimiB:

What is a foil cap? sometimes tech-speak and jargon doesn't travel well and I've never before read that term in any engineering text. <smile>

[Ears]

Also for that matter, [off thread topic], what is meant by "snubber" to describe caps in the ODS overdrive cct? I've run it past two professional electronic techs working in air traffic control systems, neither of their first guesses or explanations fitted the Dumble cct.

[mlp-mx6]

Foil cap = NON-electrolytic cap. Like an orange drop, etc.

"snubber" = actual misuse of the term. However, in this context it means the capacitor connected (usually on the tube socket) between plate and cathode. It is actually a plate bypass cap. It bleeds some highs to ground, but sounds different than the ones that are mounted across the plate resistor as in some Boogies (and others).

[novosibir]

Thanks mlp-mx6

Yes, foil caps are all tubular style caps like i.e. SoZos, Mallory 150's, the TAD Mustard clones, original Philips Mustards, aso. By principle all caps with axial leads, which might be wound with a Polyester, Polypropylene, Polystyrene, Polycarbonat and some other types of foil like i.e. paper (paper in oil caps).

All the Xicon Polypropylene and SBE Orange Drops with the radial leads are foil caps as well. And to be correct, actually all electrolytic caps are foil caps as well - wound with a very very thin aluminum foil. But in this case usually nobody says 'foil cap' and might lead to confusion.

Just let me explain/repeat some other often used terms, used for tube amps:

Snubber cap: as mlp-mx6 already said, a small cap from plate to cathode, to reduce excessive highs

Fizzy cap: A small ceramic or Silver Mica cap between both plates of the PI stage (Long tail pair), usually a 47p in Marshalls and Tweed Fenders

Bypass cap: This term is mostly used for the cap across the cathode resistor. But also for a cap across the plate resistor or across any other resistor in the amp's layout

Swamp resistor: A resistor in front of a tube's control grid (with the purpose, to form together with the tube's input capacity a low pass filter to cut off some highs)

Slope resistor: The resistor in the tone stack to the mid & bass caps

Tail resistor: The resistor below the common cathode resistor of a PI stage (Long tail pair), usually a 10K, 22K or 47K, in D-type amps a 24K

Only to mention a few for the moment.

Larry

[skyboltone]

Thanks mlp-mx6

Yes, foil caps are all tubular style caps like i.e. SoZos, Mallory 150's, the TAD Mustard clones, original Philips Mustards, aso. By principle all caps with axial leads, which might be wound with a Polyester, Polypropylene, Polystyrene, Polycarbonat and some other types of foil like i.e. paper (paper in oil caps).

All the Xicon Polypropylene and SBE Orange Drops with the radial leads are foil caps as well. And to be correct, actually all electrolytic caps are foil caps as well - wound with a very very thin aluminum foil. But in this case usually nobody says 'foil cap' and might lead to confusion.

Just let me explain/repeat some other often used terms, used for tube amps:

Snubber cap: as mlp-mx6 already said, a small cap from plate to cathode, to reduce excessive highs

Fizzy cap: A small ceramic or Silver Mica cap between both plates of the PI stage (Long tail pair), usually a 47p in Marshalls and Tweed Fenders

Bypass cap: This term is mostly used for the cap across the cathode resistor. But also for a cap across the plate resistor or across any other resistor in the amp's layout

Swamp resistor: A resistor in front of a tube's control grid (with the purpose, to form together with the tube's input capacity a low pass filter to cut off some highs)

Slope resistor: The resistor in the tone stack to the mid & bass caps

Tail resistor: The resistor below the common cathode resistor of a PI stage (Long tail pair), usually a 10K, 22K or 47K, in D-type amps a 24K

Only to mention a few for the moment.

Larry

Omar! Sticky this in Tech Talk please?