ASR-444 Stromberg Carlson: Channel A Deficient Treble After Rebuild

[Grid]

While in phono inject a signal into the 12AX7 on pin 1 or 6 to isolate the problem, pin 1 is the first section, pin 6 is the second, You can also check voltage on those pins as well. and compare to the other channel. I'm going to bed for a while, I'm on nights for another week.

(Continued...) Another development. You mentioned those 47 pf caps. I have to confess I left two in the amp because I ran out of them. One of them is on the treble control. I lifted it, and just for the hell of it I jumpered in an .0047. Treble increased noticeably. I'm going to order more of those 47 pf caps. It seems to me the original one I left on there possibly was open or damaged. I remember, since the leads were so short, the cap was sweating when I soldered it it. So i may have damaged it.

 

[s-petersen]

That is great news! you may want to recheck your values according to this chart.
A 47pf cap is .000047
http://www.justradios.com/uFnFpF.html

 

[Grid]

Oh, yes, I use that chart to death, lol! Thank you.

By the way, the other old 47pf I left in was, yep, on the 6U8. I'll order and should have them by the weekend. You know, it sounds so much better even now. I almost could live with it. Been listening to mono. Stereo will be more critical, I know.

 

[s-petersen]

I would replace the ceramic caps with polypropylene(or polystyrene) or silver mica, ceramic is not very good.

 

[Grid]

I would replace the ceramic caps with polypropylene(or polystyrene) or silver mica, ceramic is not very good.

Yes, I believe my replacements were polypropylene and a couple silver mica. All silver mica would be nice but they sure are expensive, eh?

 

[s-petersen]

Not really bad, I've ordered them from the auction site,(in quantity 10)and they measured correctly.

 

[Grid]

Not really bad, I've ordered them from the auction site,(in quantity 10)and they measured correctly.

Well, a lot of people just keep the originals and say they last forever. But for this project, I just replaced everything. New ceramic has to be better in the long run. I just checked. Most of what I bought were ceramics by Murata. https://www.mouser.com/ProductDetail/81-DE21XSA470KN3AY2F

 

[gadget73]

Ceramic function almost forever, but IMO they sound bad. Very rarely will you hear me say I don't like the sound of a part, or honestly even notice it, but ceramic caps are one of the rare exceptions. Unfortunate, since I hate replacing parts that work properly. I also tend to be more critical of components placed outside of a feedback loop, such as things in a tone control circuit. There isn't any real mechanism to correct for any non-linearities in the part so its more audible or at least measurable.

 

[Grid]

Ceramic function almost forever, but IMO they sound bad. Very rarely will you hear me say I don't like the sound of a part, or honestly even notice it, but ceramic caps are one of the rare exceptions. Unfortunate, since I hate replacing parts that work properly. I also tend to be more critical of components placed outside of a feedback loop, such as things in a tone control circuit. There isn't any real mechanism to correct for any non-linearities in the part so its more audible or at least measurable.

hmmm... so i guess i'm not fully hearing the fidelity the amp can make. i've been thinking about finally investing in a scope. suggestions for cheap decent?

 

[gadget73]

I've never been able to measure what I don't like about ceramic caps, I just find them to be harsh sounding. Not sure if its because of that piezoelectric thing or what, but they just bother my ears.

Cheap and decent scope is generally the realm of analog CRT stuff. People don't want them anymore, so good ones can be had for small money. Mine is a BK Precision that I got for a song some years ago, but really any known maker of test gear makes a scope thats usable. I wouldn't mind upgrading to a Tek or HP that will do on-screen direct readout measurements but I haven't tripped over one for basically free yet.

 

[Retrovert]

BaTiO3 is a horrible material for capacitors because it piezoelectric, microphonic, pyroelectric (temperature changes result in a voltage potential across the electrodes), has a non-linear DC bias problem which reduces the capacitance with applied DC voltage, and a time-dependent dielectric breakdown from applying a constant DC bias voltage, which is in addition to the reduction in capacitance, and is hygroscopic.

A BaTiO3 capacitors would never be considered audiophile grade, even with a liberal interpretation for "audiophile grade", when used in the signal path. The main use for such capacitors is decoupling in high-speed digital circuits where the horrid properties do not matter and the item is usually disposable after a few years.

Film capacitors are inexpensive and small, so no reason to leave BaTiO3 in the equipment.

 

[EastPoint]

Ceramic disk caps drop in value over time, fairly often. I've seen some that were under by 30-35%. I've seen some that went up, too, and some with substantial voltage leakage.

 

[Grid]

I've never been able to measure what I don't like about ceramic caps, I just find them to be harsh sounding. Not sure if its because of that piezoelectric thing or what, but they just bother my ears.

Cheap and decent scope is generally the realm of analog CRT stuff. People don't want them anymore, so good ones can be had for small money. Mine is a BK Precision that I got for a song some years ago, but really any known maker of test gear makes a scope thats usable. I wouldn't mind upgrading to a Tek or HP that will do on-screen direct readout measurements but I haven't tripped over one for basically free yet.

Makes sense about CRT. Thanks again.