Tiny Terror: 216 uF capacitance for just 15 Watts?

[jmaf]

There's an Orange "Tiny Terror" schematic floating around, it seems to be accepted as the correct schem for this pretty neat amp.

What caught my attention is the amount of capacitance on this schem.

100 uF at 325 V power section reservoir,
then 47 uF at 320 V for +B1,
then 47 uF at 290 +B2, and finally 22uF at 265 V for the first gain stage(1 Watt...).

Total: 216 uF

Laney LC-15 use a 50 uF at 300 V for +B, then a couple 15 uF's later on for +B*... Other 15 watters I've seen share similar values.

Are any of you who are more familiar with this amp able to tell me if these values are correct? Thanks very much in advance.

[fyl]

The values are correct for the standard version (the hardwired TT uses slightly different values).

[Prairie Dawg]

There's an Orange "Tiny Terror" schematic floating around, it seems to be accepted as the correct schem for this pretty neat amp.

What caught my attention is the amount of capacitance on this schem.

100 uF at 325 V power section reservoir,
then 47 uF at 320 V for +B1,
then 47 uF at 290 +B2, and finally 22uF at 265 V for the first gain stage(1 Watt...).

Total: 216 uF

Laney LC-15 use a 50 uF at 300 V for +B, then a couple 15 uF's later on for +B*... Other 15 watters I've seen share similar values.

Are any of you who are more familiar with this amp able to tell me if these values are correct? Thanks very much in advance.

I don't think adding the values up is germane to the subject. It doesn't sound excessive to me. Prolly make for a tight and focused bottom end, all things being equal.

[fyl]

It doesn't sound excessive to me.

Ditto here. Most guitar amps are fitted with very poorly designed power supplies - most are derived from 40 or 50-years old schemos, from a time when playing styles were much more gentle and large elcos costed a small fortune.

Most ghosting and flubbing problems disappear when you lower coupling as well as cathode bypass caps *and* use larger filtering caps in a proper distributed way (1 tube = 1 filtering node, preferably 1 tube section = 1 filtering node).

[Gee]

I suspect those caps were chosen more for availability/cost/packaging than tone chasing. I am pretty sure the Hard Wired TT uses more conventional (for this type of amp) values.

[Prairie Dawg]

[QUOTE=fyl;163358+


Most ghosting and flubbing problems disappear when you lower coupling as well as cathode bypass caps *and* use larger filtering caps in a proper distributed way (1 tube = 1 filtering node, preferably 1 tube section = 1 filtering node).[/QUOTE]

Do you have any resource links or specific information on this subject? I have a customer's reissue bassman that I'm fighting that battle with and I think it may be in part related to power supply capacitances.

[fyl]

Do you have any resource links or specific information on this subject?

Alas, there's very little MI-specific info on the web or in specialized books - a few pages in various TUT's.

I have a customer's reissue bassman that I'm fighting that battle with and I think it may be in part related to power supply capacitances.

Which model? What are the problems?

(Sometimes using a 12AY7 instead of the crappy factory-supplied 12AX7 for V1 can work wonders)

[jmaf]

I suspect those caps were chosen more for availability/cost/packaging than tone chasing. I am pretty sure the Hard Wired TT uses more conventional (for this type of amp) values.

I can understand why they'd increase capacitance. When you mention tweeds, the '59 had 80 uF total capacitance for 40 Watts. That too is a bit underdimensioned. But 216 uF for 2 EL84's?

Here's an extreme comparison: some 100 Watt JCM800's had around 500 uF in 5 blue LCR's(50+50), which to me was already exaggerated. But BIGGER, MORE was a mark of the 80's.

Considering that power in caps is directly proportional to cap size, the JCM 800 which like I said was overdesigned, would have 1440 uF capacitance following the Tiny Terror uF per Watt proportion....

Since other members have confirmed that these are the correct values, I would agree with Gee that they probably bought a large lot of these 100uF's and deployed them. There is very little engineering sense in so much capacitance. After a certain level the amp won't pull more current, the excess cap size is just a waste as the power supply impedance falls near zero.

[Hardtailed]

In hi-fi terms, this is really low capacitance!

I think you're seeing this the wrong way. For one thing, don't compare preamp filter caps to output power. These only see a few milliamps of current and have almost zero impact of the current available to the output valves.

You could have 1000uF on the preamp and the amp would still sag easily with a 16uF as the main filter for the output tubes.

Some amps use very high capacitance in the preamp, some don't. I haven't messed with this enough to really comment how that affect the preamp.
Interesting thing is that the Soldano SLO, which has 220uF of filtering for the plates (more than a JCM800), uses measly 10uF caps in the preamp. On the other hand, a Vox AC30 which has a wimpy 16uF feeding the plates, uses a 32uF for the Top Boost circuit.

You're also missing an important point about the JCM800: some of those caps were connected in series (for voltage handling). Many 100W Marshall with 5 or 6 cap cans really had 50uF on the plates: they connected the two sections of 2 50/50 cans in parallel, then those two cans in series (that's 100uF in series with 100uF, total 50uF)
On the other hand, the 50W model had just one can in parallel (they had lower voltage), meaning the 50W model had MORE filtering than the 100W at 100uF.
The other cans are for the preamp: again, this has no impact on the power amp.

There is no magic formula of wattage vs capacitance.

And there is no such thing as too much filtering if that is the tone you're looking for. The Tiny Terror was never designed to sag like an old Fender Deluxe.

[jmaf]

You're also missing an important point about the JCM800: some of those caps were connected in series (for voltage handling). Many 100W Marshall with 5 or 6 cap cans really had 50uF on the plates: they connected the two sections of 2 50/50 cans in parallel, then those two cans in series (that's 100uF in series with 100uF, total 50uF)

What JCM 800 was that?

There is no magic formula of wattage vs capacitance.

You're right that it's not magic!

Thanks for your feedback.

[jmaf]

There's this picture of an assembly: http://www.zikinf.com/_gfx/matos/dyn...-edition_2.jpg

The 3 pots are double pots. But the schematic that is going around the WWW is 2 double pots, one regular for the tone. Looking at it closely, it seems they used whatever parts they had lying around on this assembly....that double pot seems to be wired as a single.

I think the caps have varied on the schematic as well. See after the 150R ceramic resistor we have 33 uF cap, in the schem it's a 47uF.

That F&T cap seems to be a 220uf? http://www.c3amps.com/Photos/Parts/FT-220-385_lg.jpg - If so, that's one heck of a cap for a 15 watt stage.

This neat amp, I look forward to building one soon.

[J M Fahey]

Please do not add up all capacitance values and think it means something (except, perhaps, to the accountant who's checking cost sheets).
The "power" filtering is the one fed straight from the rectifiers and going to the output transformer center tap, and its value can and will influence perceived sound.
Preamp capacitors are hum (and motorboating) killers , the larger the merrier in general terms.

[jmaf]

Please do not add up all capacitance values and think it means something (except, perhaps, to the accountant who's checking cost sheets).
The "power" filtering is the one fed straight from the rectifiers and going to the output transformer center tap, and its value can and will influence perceived sound.
Preamp capacitors are hum (and motorboating) killers , the larger the merrier in general terms.

I know the preamp caps don't phone home any current.

The front wheels serve a different purpose than the ones in the back, but we still call them 18-wheelers, right? It's a seat of the pants comparison, no more than that.

Power supplies are very similar, so when I said it has 216uF total capacitance, if you go cap by cap you'll see that most of the time the proportion holds. If it were a JCM800 and kept the proportion per watt, it'd have 1440 uF, a senseless measure to illustrate that this 15 Watter has bigger sag fighting ambitions than Laney's, for example.

[Prairie Dawg]

Alas, there's very little MI-specific info on the web or in specialized books - a few pages in various TUT's.



Which model? What are the problems?

(Sometimes using a 12AY7 instead of the crappy factory-supplied 12AX7 for V1 can work wonders)

It's a white board number. It came out of a closet, hardly used, my friend got a great price on it but it sounded lousy. I checked all the tubes on my Hickok, and proceeded to install a bias adjust control-the bias was set very low, about 12 ma each. Put it up to about 32, and on further inspection found that the solder joint on one of the screen resistors was nonexistent. As a point of information the solder was there-the resistor lead had not tinned. I reassembled it and it seemed OK. It came back with a tonal artifact-a sort of fizzle after a hard note was played. I then went and tried every combination of preamp tubes known to man without positive results., and I have a very good tube collection acquired through 25 years of antique and vintage radio work.

Last time I thought I had it, because I saw a quick arc in the rectifier tube-Sovtek. That went into the trash and a new JJ GZ34 went in. No change.

So now I'm down to replacing the electrolytics and taking it and my scope down to Rock Island for a bit of scope training-which is something i need badly. It's coming back Sunday.

[Hardtailed]

What JCM 800 was that?

Take the ubiquitous 2203 (single channel 100W) for example:
http://www.drtube.com/schematics/marshall/2203u.gif

Notice that after the bridge rectifier it hits 2 100uF capacitors connected in series. By your "math" that would amount to 200uF, but series connection is like resistors in parallel: it totals 50uF!
The 2 100uFs were usually a pair of 50uF (in the same can) connected in parallel together. So you have 2 50/50 cans but the total capacitance is... 50uF!