Simms Watt 100w Head

[josegrad]

The three big electrolytic capacitors show up in the images as 100uF, no idea the blue one, and 16uF.




I'm not 100% sure where those are in the schematics.
Any hints?




Thanks.

[nickb]

I've labelled your pic with the node letter and the capacitance value used in the schematic:

[josegrad]

I've labelled your pic with the node letter and the capacitance value used in the schematic

Thanks nickb, I'll start looking for replacements.

[josegrad]

Light bulb limiter ready. Capacitors changed. New fuses in place.

I'm quite close to start the amp again. With a speaker and a single hand of course.

But it is hard to place it somewhere where nothing touches the bench I have.
I guess there's no danger in placing it on the transformers like in the image below.



Cheers.

[g1]

No danger. Make sure the tubes don't burn/melt anything, and make sure it's secure enough that if you scare yourself, you don't end up with it sitting on your lap, or broken on the floor.

[josegrad]

No danger. Make sure the tubes don't burn/melt anything, and make sure it's secure enough that if you scare yourself, you don't end up with it sitting on your lap, or broken on the floor.

Thanks g1. Yeah maybe I'll put it a bit higher on the bench so there's more space below the tubes.
I'll get the crocodile clips in place to discharge the caps before touching anything in between when needed.

It is close by the door, in case of danger I'll open the door and throw it away

[J M Fahey]

Ha,

Did I mention I'm in Finland? I can find trees and lakes of any size.

And also these bulbs I can get easily:

[ATTACH=CONFIG]50727[/ATTACH]

But 100W old style bulbs are harder to get. Hmm, I bet the Russians have

Cheers.

I bet a bulb which irradiates 70% of energy into the room as infrared waves is an asset, not a liability, if we are talking sub-zero Countries.

Which of course includes Finland

I always suggest using 100/150/250W halogen "stick" lamps which are widely available anywhere without special ordering.

[josegrad]

Right.

I have now verified that the light bulb limiter operates properly by using another amp.

When I use it with this amp and I switch ON the mains, the bulb stays on all the time.
I have not yet switched on the stand by one.
Only the one on the right switched.



Is it as bad as it looks, or should I switch both ON?

Cheers.

[josegrad]

Actually. When only the mains are ON the bulb stays light, but I can still look at it. If I light the bulb alone you cannot look at it.

I turned the light off and I can see the the 4 big valves are lighting up a bit.

I guess I could leave it on for a while, and then turn ON the other switch.

[Chuck H]

If the bulb is lighting brightly with the standby switch in the silent position you may have a bad rectifier or main filter cap. If you lift the PT secondary leads from the rectifier and the bulb lights brightly you have a shorted PT.

Don't flip the standby switch into play mode yet and don't remove the bulb limiter from the test circumstances yet.

[J M Fahey]

Agree and add: please try amp as-is, same bulb limiter, etc. , but pulling all tubes from it, so we remove filament load, which is significative.

What happens with lightbulb brightness?
Stays the same?
We have less? (itīs somewhat darker).

The point I want to check is that since tube amps in general are power guzzlers even at idle, and that Simms Watts may be even more so, I want to know whether that idle lightbulb brightness comes from a lossy transformer or simply we "should" be using a somewhat higher wattage bulb.

[josegrad]

I removed all the valves from the amp, 8 in total.

When switching ON the mains the light bulb didn't light up at all. To my surprise the front bulb of the amp did light up, but only for a couple of times, then when I tried again it didn't light up anymore. The bulb limiter didn't light up at all as I mentioned.

@chuck, does PT stands for Power Transformer? Sorry, I'm not a pro so I can't get all the acronyms.

Thanks for the hints.

[Chuck H]

I removed all the valves from the amp, 8 in total.

When switching ON the mains the light bulb didn't light up at all. To my surprise the front bulb of the amp did light up, but only for a couple of times, then when I tried again it didn't light up anymore. The bulb limiter didn't light up at all as I mentioned.

@chuck, does PT stands for Power Transformer? Sorry, I'm not a pro so I can't get all the acronyms.

Thanks for the hints.

Yes, PT is an acronym for power transformer.

It's possible that the pilot lamp has a bad or dirty connection? I don't see the pilot lamp in the schematics.?.

That the bulb didn't light at all is actually impossible if even the pilot lamp was on. But it could be that when the pilot lamp was on that the limiter bulb was so dim that you couldn't tell it was lit at all.

I'm confused by the results. Just to confirm, with the tubes in and the standby switch in the silent position the limiter bulb glows brightly, and with the tubes out and the standby still in the silent position the limiter bulb doesn't glow at all.

[J M Fahey]

I'm confused by the results. Just to confirm, with the tubes in and the standby switch in the silent position the limiter bulb glows brightly,

Define "brightly" ... and josegrad never said that, you just assume he did.

No, not brightly at all, we are having a language or interpretation barrier here.

My take, and that is why I asked for tubes removal to minimize load, is that josegrad just mentions "the filament being visible" , not the same:

When I use it with this amp and I switch ON the mains, the bulb stays on all the time.

NOT "full on bright" (as if connected straight to mains in a desk lamp) which is a very different thing.
In fact josegrad mentions *two* brightness levels:

Actually. When only the mains are ON the bulb stays light, but I can still look at it.

In my book that means "attenuated" brightness, meaning amp which is in series with bulb is NOT a short.

If I light the bulb alone you cannot look at it.

*
I understand that as full brightness, bulb straight into mains, no amp involved.
In fact I asked for and got a *third* brightness level :

I removed all the valves from the amp, 8 in total.
When switching ON the mains the light bulb didn't light up at all.

which means idle current, with no tube filament load, is not enough to heat bulb filament enough to be visible in daylight.
I *guess* it will be dark red if seen in the dark.

In a nutshell, so far I guess PT, main rectifiers and filter caps are fine.

josegrad should (carefully, DEADLY voltage there) measure voltage with Standby OFF, just before the switch.
Would not be surprised to find some 400 V or more there.
Which would confirm my earliest assumption.

As of the intermittent pilot light, no big deal, tarnished/rusty/dirty contacts are common after 48 years.

[Chuck H]

You're probably right Juan. I interpreted his description "I can still look at it" not so much as attenuated, but barely attenuated. Otherwise why mention it like that.?. So could be a bad assumption on my part. My concern was a heavy current load with no high voltage on the tubes. But with eight tubes in the amp I suppose the filament load could get the limiter bulb pretty bright.