capacitor help wem dominator

[Twincam]

Hi I can't identify the blue cap on the rights values. uf or voltage nothing written on it I think it's a 50uf but I can't find the right schematic for a wen dominator 25 bass. I know all the dominators' were similar but best get it right. I have a replacement cap for the larger one.

If anyone can tell me I would appreciate that.

[URL=http://s330.photobucket.com/user/Twincam2008/media/Mobile%20Uploads/WP_20160509_17_22_19_Pro_zpsicdnwcqi.jpg.html][IMG]http://i330.photobucket.com/albums/l415/Twincam2008/Mobile%20Uploads/WP_20160509_17_22_19_Pro_zpsicdnwcqi.jpg[/IMG][/URL]

[Twincam]

It's ok I've found it thanks is a 32uf 350v if anyone reading this needs to know in future, the large one is a 50+50uf 350v

[Dad3353]

I presume you're wanting to change these simply by precaution..? I know they can often age badly (I have valve amps, too...), but those don't look, from the photo, to be in bad shape at all. Just sayin'.

[Twincam]

[quote name='Dad3353' timestamp='1462815051' post='3045927']
I presume you're wanting to change these simply by precaution..? I know they can often age badly (I have valve amps, too...), but those don't look, from the photo, to be in bad shape at all. Just sayin'.
[/quote]

The large one is bubbled and slight leakage in the middle I missed it a few times, you can just see white on top of the bubble. And the other is in good nik but will be changed as a precaution.
The amp is buzzing away through the speaker but working well, it sounds like the power line 50/60hz way so I assume it's the burst filter cap especially as it doesn't change with volume. It could be a valve ac heater issue or some other grounding issue. But since the amp is original never serviced and the cap is burst then I will start there. Was £18 odd quid for both the caps.

Oh and if anyone in future reads this if changing valves on a wem dominator from the 70s unless using original mullards with pin 1 and 2 connected internally, you need to move the connections on the actual socket from p1 to pin 2 if you don't the tubes have no bias!!!! And the amp will hardly work too before the valve goes in a bad way!

Edited May 9, 2016 by Twincam

[icastle]

If you want to discharge the cap, best way is to get a couple of high voltage ceramic resistors -connect a crocodile clip to either end and clip it to both ends of the electrolytic.

Leave it alone for a minute or so.

Any residual charge within the cap will be shorted, through the resistors which turn the charge into heat.

[Twincam]

[quote name='icastle' timestamp='1462819783' post='3046022']
If you want to discharge the cap, best way is to get a couple of high voltage ceramic resistors -connect a crocodile clip to either end and clip it to both ends of the electrolytic.

Leave it alone for a minute or so.

Any residual charge within the cap will be shorted, through the resistors which turn the charge into heat.
[/quote]

I use the resistor to ground method. It works although got a bit of a spark off the small cap even though I check them with a multimeter.

[icastle]

[quote name='Twincam' timestamp='1462821181' post='3046040']
I use the resistor to ground method. It works although got a bit of a spark off the small cap even though I check them with a multimeter.
[/quote]

Your resistors are perhaps too low a value.

You can't check it with a multimeter though - you're looking for current, not voltage.

[Twincam]

But without voltage there would be no current? So no or under ten volt safe to handle? That is the way I've seen them tested after drainage.

I used to test with my tongue that didn't work so well. (obviously never lick a capacitor!)

[Beer of the Bass]

Checking voltage between the cap positive and ground is fine IMO, since it's a voltage difference that causes current to flow anyway. I'll often discharge the caps by using a simple clip lead to connect the plate of the first preamp valve (pin 1 on an ECC83) to ground. The caps then discharge through the plate resistor (usually in the 100k ohm range), and the lead can be left in place when working. Obviously, it's still important the check that they've discharged, and in some amps they won't discharge using this method unless the standby switch is closed.

[icastle]

[quote name='Twincam' timestamp='1462824631' post='3046096']
But without voltage there would be no current? So no or under ten volt safe to handle? That is the way I've seen them tested after drainage.
[/quote]

As little as 10mA is enough current to give you a nasty jolt.

A taser uses high voltage and low current.
An emergency light uses low voltage and high current.

Both can give you a shock.

Think of voltage as pressure and amps as movement and it'll become clearer.

[Beer of the Bass]

In this application I would just check the voltage on the caps, and not touch anything until it has dropped to single figures. I have not heard of any working valve amp technician doing anything different, so I'd say this is over complicating things.

[Dad3353]

An anecdote..? Yes..? Oh, good; sit yourselves down comfortably, but this won't take [i]that [/i]long.

I was apprenticed to BEA (British Airways, now...); we shared training with BOAC bods. One of these (John Butler...) was the punching ball for all of the cruel japes that our fellow apprentices thought up, and a bit of an dummy, if truth were told. One day, he came in with an old, very old, portable radio. No, not a transistor, this one was a valve radio. Inside was the blue Ever Ready battery, with a four-pin socket. These batteries have two parts: a 1.5 volt part for the heater required for valves, and a 90 volt part for the HT. Now, then; how do we check trannie batteries to see if they're OK..? Yes, that's right; we touch the terminals to our tongue. A tingle, and it's OK. So, how does Butler propose to check the 90 volts..? Right again, he's about to put his tongue to it. All our colleagues are watching, egging him on, indeed. I was able to stop him, just in time. A quick explanation as to why it was probably not a Good Idea, he laughs sheepishly and desists. His eyes light up, though, after a second or two's reflection. "But I can check the other part, can't I..? It's only 1.5 volts..! That can't hurt, surely..?" Another explanation was necessary, using the analogy of a 6 volt motorbike battery. Would one like to apply [i]that [/i]to one's tongue..? Not a Good Idea either, as the potential current flow, despite the low voltage, would probably burn the tongue away. The others were disappointed, though, as they wanted to see just how far the darned fool would go. In the end, we tested with an Avometer; he would have been seriously hurt.
It's not just the tension, [i]per se[/i], it's how much energy could be released at once that can be dangerous.
OK, break-time over. As you were, folks; thanks for your patience...

Edited May 9, 2016 by Dad3353

[Twincam]

I like a good anecdote.
I'm wondering if I would of let him lick the battery. I think I might of let him.

[Dad3353]

[quote name='Twincam' timestamp='1462832130' post='3046186']...I think I might of let him.
[/quote]

[luckydog]

This reminds me of Dumb and Dumber, where one of them ends up with his tongue attached to a ski lift.......

Anyone heard of the Darwin Awards, given posthumously to those who remove their genes from the genepool in the most outrageous ways ? It's such a bad idea to use yer tongue to check charge on caps as to beggar belief, and would qualify for the Darwin Awards for sure, being highly likely to kill or mame....

Back in the 70s I worked in Sound City's repair shop in the basement on Shaftesbury Ave, and saw a lot of Dominators. They didn't have much reputation at the time, but now have a following and certainly a unique sound - the tone stack is essentially from a Bassman IIRC. Again, if memory serves, there were one or two favourite spots for dry joints and cracks/track breaks near the supports, worth a check ? HTH!

LD

Edited May 10, 2016 by luckydog

[Phil Starr]

I learned to treat power supply caps the hard way. I used to discharge them with a screwdriver across the terminals? At 18 anything that sparked was fun, and it was quick. I got careless one day and managed to touch the live end before the earth. DC shocks are much more interesting than AC and this one shocked me hard enough to throw me back across the room. Jumped out of my skin again when the screwdriver landed on me.

[JapanAxe]

[quote name='Twincam' timestamp='1462824631' post='3046096']
obviously never lick a capacitor!
[/quote]

[i]Now[/i] he tells us!

[pfretrock]

[quote name='Twincam' timestamp='1462819431' post='3046017']
The amp is buzzing away through the speaker but working well, it sounds like the power line 50/60hz way so I assume it's the burst filter cap especially as it doesn't change with volume. It could be a valve ac heater issue or some other grounding issue. But since the amp is original never serviced and the cap is burst then I will start there. Was £18 odd quid for both the caps.
[/quote]

That is a full wave rectifier, so any capacitor problems would give a 100Hz buzz. Just thought i'd mention it. I'd probably replace the caps anyway as it looks like it has vented.

[pfretrock]

[quote name='Twincam' timestamp='1462824631' post='3046096']
(obviously never lick a capacitor!)
[/quote]

I once licked a flux capacitor. Who knows why I did it?

[Dad3353]

[quote name='pfretrock' timestamp='1463323112' post='3050443']
I once licked a flux capacitor. Who knows why I did it?
[/quote]

That rings like a line from ISIHAC... "The last thing I remember..."..!

[Twincam]

Caps replaced, heater wires sorted, bias redone and components replaced, new valves.

Amp is much better, less noise than some modern ss heads I've had.

However the slight overdriven sound is still there much less than before, but it's there from low volume and doesn't change till much higher volumes, so I'm not sure if there's an issue or if it's just the amps natural tone. It's not horrible just a nice little bit of drive going on. I have heard this amps are old school sounding and not clean amps.

You can hear the amp in this months noodle comp

[gelfin]

When I used to work in a Hi Fi shop we used to get the engineer to charge up caps for us.
We had an ar$e of a manger so we would slip them into his pocket and just wiat for him to put his hand in.

[gelfin]

Self same engineer used to make all sorts of iffy devices for us.

The night nuiscance. Construcetd in a ciggarette packet, an old type earphone a light sensitive transistor a battery
and some other bits.

Leave it in someones bedroom, while it was light or the light was on it would remain silent.
As soon as it was dark it would make a noise like an angry mosquito. Target person switches light on to find it
and it goes silent.

I still have it somewhere

Edited May 15, 2016 by gelfin

[HowieBass]

[quote name='Twincam' timestamp='1463339468' post='3050640']
Caps replaced, heater wires sorted, bias redone and components replaced, new valves.

Amp is much better, less noise than some modern ss heads I've had.

However the slight overdriven sound is still there much less than before, but it's there from low volume and doesn't change till much higher volumes, so I'm not sure if there's an issue or if it's just the amps natural tone. It's not horrible just a nice little bit of drive going on. I have heard this amps are old school sounding and not clean amps.

You can hear the amp in this months noodle comp
[/quote]

I'm wondering what valve you have in the preamp stage - I've read that there's a lot of variation across the different makes even when they're supposed to have the same gain factor (eg. 12AX7 or ECC83 valves) - maybe this could be the source of the slight overdriven sound you're hearing?

Some useful info here http://www.worldtubecompany.com/mm5/merchant.mvc?Screen=TF-2 and also a guide to the gain factors of various valve types here http://www.thetubestore.com/Resources/Guitar-Amp-Info/Gain-Factor

[Twincam]

[quote name='HowieBass' timestamp='1463349036' post='3050724']


I'm wondering what valve you have in the preamp stage - I've read that there's a lot of variation across the different makes even when they're supposed to have the same gain factor (eg. 12AX7 or ECC83 valves) - maybe this could be the source of the slight overdriven sound you're hearing?

Some useful info here http://www.worldtubecompany.com/mm5/merchant.mvc?Screen=TF-2 and also a guide to the gain factors of various valve types here http://www.thetubestore.com/Resources/Guitar-Amp-Info/Gain-Factor
[/quote]

I have a jj ecc83s but with the mullard valve in the pre it was about the same. I read it is easy to overload the front end with a modern bass. I do like the sound a lot so no worries just concerned I've missed something.