70's vs. 80's power amp...

[talbany]

I thought a inductor opposes a change in current, which is why it is used in a power supply, keeps the current from dragging down too fast, the result being that it helps the filter caps maintain a current source for the amp.
Is that wrong?

Tom

Yep!! The current in an inductor cannot change instantaneously; that is, inductors tend to resist any change in current flow. This property makes them good for use as filter elements, since they tend to "smooth out" the ripples in the rectified voltage waveform...Like you describe...

Tony

[wjdunham]

Tom, I learned through much experimentation what the pro's already knew - the choke definitely has the biggest effect on the low end mud, but remember, that's only for mud caused by driving the power amp really hard. I was not using the OD channel during most of this testing, it was the cleans cranked to Pete Townshend levels through a 2x12 EVM12L or an old 60's Marshall 4x12 with 25W greenbacks (a truly kick-ass cabinet). I spent a lot of time twiddling he overdrive entrance and couplers to get it nice and tight at moderate volumes, it wasn't until I had a few gigs with the amp that I started homing in on the choke vs. RF mod resistor.

As for the bias feed changes, my understanding is that will only help if you again are really cranked and running into that nasty blocking distortion. I've found it's a little harder to diagnose, since that same nasty sound can come from a few different things, speaker overload, broken shit in your rack, as well as the bias sag induced by the PT grids drawing current during overdrive. It doesn't do much for cleaning up mud if you are properly biased and not playing at The Who volumes. I will find out more tonight. I chased my tail quite a bit due to a bad rack mount tuner, which for some reason when driven with a hot signal it broke up similar with a similar nasty, farty distortion. Now that I junked that, I can see how the amp does. Will report back with my impressions.

[Structo]

Looking forward to your review.

About a year ago I was messing around with my amp and I cranked the volume and master to 10.
I think I experienced blocking distortion at the time because the amp actually started cutting out a bit when I was throwing power chords at it.
(I quickly turned it down)

The amp was fairly young at the time and I wisely don't turn the amp up to those levels anymore.
There has been a lot of changes since then including a new OT (Prosonic) and other tweaks.
I believe it was essentially the stock layout at the time which is more geared towards 6V6 power tubes. Now it has been modded completely with 6L6's in minds so it is "more better".

[greiswig]

I look forward to hearing more, and to seeing how you added it. Also, did you play with the dropping string afterward? If not, I would expect the voltages on all segments to have risen somewhat, which could be at least part of the reason it sounds different.

Bill, any chance you could comment on these items?

[wjdunham]

I measured the voltages after installing the choke, I din't think it made much of a difference on the preamp tube voltages. I didn't do a strict before and after comparison, but when I went back and measured V1 and V2 they seemed a bit low (185, 190), so I lowered the 22K to 18K to get them up in the 190-200 range.

I had the amp cranked all night and held up great with the changes. The choke for my taste and style of playing is a far better choice. I don't play in a relaxed style where a little sag and softness is maybe desirable. I prefer a very tight and stiff amp, which this experience has tought me. No problems with graininess or loss of gain late in the gig, so Im going to keep the 180K/.05u bias feed in there.

For reference, my band is a cover band doing a lot of 80's stuff, the Cars, Doobie Bros, Jesse's Girl, Journey, Fleetwood Mac, ACDC, with some 90's stuff like No Doubt and Sublime. I love the D-Style amps because I can get such a wide range of tones, at any volume level. The strat tone comes through great for a blues oriented song, and a LP for the more rock oriented sounds like a cranked marshall. Marshalls sounded great for one style, Fenders for the other, but nothing could really cover such a wide range. With the RF mod resistor, I couldn't really get it to sound like a Marshall, now it's pretty close. and if I play in the right style, it can even sound like a Dumble I had foot pedals up the ying, and they're all gone now.
Bill

[talbany]

Bill

Glad you got her ironed out..A great example of setting the amp up for it's intended operation..
Been hanging around here like forever now I read quite a few posts where people mention a mod they like..but never mention how that mod effects and amps performance over the entire operating range of the amp..A good lesson for sure...Good Luck!!

Side note:.. As mentioned in Tone Quest Report.. Stevies famed Vibroverb (which was stolen)..The amp was reported as sounding not so good at lower volumes.. set on 666 the amp morphed into well we all know..

Tony

[BobW]

I thought a inductor opposes a change in current, which is why it is used in a power supply, keeps the current from dragging down too fast, the result being that it helps the filter caps maintain a current source for the amp.
Is that wrong?

Tom

Yep!! The current in an inductor cannot change instantaneously; that is, inductors tend to resist any change in current flow. This property makes them good for use as filter elements, since they tend to "smooth out" the ripples in the rectified voltage waveform...Like you describe...

Tony

I concur with you both, but the opposing change in current is what helps regulate the voltage. We're saying the same thing, just looking at it from a voltage vs. current persopective, since sag (voltage) was discussed earlier.

[talbany]

I thought a inductor opposes a change in current, which is why it is used in a power supply, keeps the current from dragging down too fast, the result being that it helps the filter caps maintain a current source for the amp.
Is that wrong?

Tom

Yep!! The current in an inductor cannot change instantaneously; that is, inductors tend to resist any change in current flow. This property makes them good for use as filter elements, since they tend to "smooth out" the ripples in the rectified voltage waveform...Like you describe...

Tony

I concur with you both, but the opposing change in current is what helps regulate the voltage. We're saying the same thing, just looking at it from a voltage vs. current persopective, since sag (voltage) was discussed earlier. 8)

Bob
I see what your saying now DOH!!
It's the magnetic field that opposes the instantanious change in current.. Like you say therefore regulating voltage...Got it..Agree!!

Tony