Ampeg ET-2B echo twin

[g-man]

Deleted

[sluckey]

Can the stock on-off switch be replaced with some sort of standby-off-on type

Yes. Doug has just what you need.

[Tom_Hull]

h

and always a good review for what to do with a standby switch.

http://www.valvewizard.co.uk/standby.html

[g-man]

Deleted

[sluckey]

But, out of curiosity, can someone explain how the DPST switch can be used for this amp? I understand how it would work for a typical amp with a single B+ supply, but this Ampeg has two separate B+ supplies (one for each side of the amp). Seems like some kind of special 3 pole switch would be needed unless both B+ can be interrupted with a single pole.

I should not have been so hasty to suggest replacing the power switch with Doug's progressive off/standby/operate switch. The two separate power supplies make that impossible. Sorry.

If you decide to add a separate standby switch you will need a DPST switch.

[Jack1962]

use 2 dpst switchs that is the way I would do it, one for power one for standby.

[g-man]

Deleted

[Willabe]

This is the bias modulation style trem I think.

Yes but only on channel 2.


       Brad   

[sluckey]

However there is a pretty loud thump and tick noise with the intensity pot above ~4. Any suggestions for reducing or eliminating that?

Do you have enough usable intensity with the pot set below ≈4? If so, you can put a 1M resistor between the pot and the 1µF cap. If not, try putting a .047µf and/or a 1N4007 across the outer lugs of the pot. Connect the diode cathode to the ground side of the pot.

[g-man]

Deleted

[sluckey]

There are no high frequencies coming from the LFO. The cap would simply smooth the 3-10Hz LFO signal. It will also attenuate it some. Many trem oscillators have smoothing caps on the LFO signal. Look at most any Fender. The diode will shunt the positive half cycle of the trem signal to ground, thus preventing the grids of the output tubes from trying to swing positive. Only the negative half cycle of the LFO will affect the output tube grids.

I've never done the diode trick but it sounds feasible. Very easy to do/undo.

[g-man]

Deleted

[sluckey]

I know there is at least 150v at that junction.

There is no dc voltage on the intensity pot. Using clip leads is fine for testing.

[g-man]

Deleted

[g-man]

Deleted

[Tom_Hull]

Hi

I thought that the amp gives out 15 watts per side.
that's 7.5 watts per tube .of clean power ?

maybe everything is working hard ..

tom

[sluckey]

Most cathode biased power tubes typically run 90% to 100% static dissipation. I would not worry too much about 70%. But I would probably increase the cathode resistors a little bit.

[g-man]

[sluckey]

I think that's workable. However, adding two diodes will keep the two power supplies isolated. Might be a good safety precaution.

[g-man]

Deleted

[sluckey]

Thanks but I don't really understand the need for the diodes. As originally designed, the rectifier grounds are essentially already connected through the chassis. So if I decide to not add a standby, would it be a safety precaution to add diodes where each rectifier currently connects to the chassis?

If you don't break that ground connection everything will last forever. But when you connect those grounds together AND open the path to ground, as is the case when in Standby mode, you have a floating circuit. If one of the supplies should fail shorted it may take out the other supply. Too many scenarios to think about. The diodes prevent a problem with one supply from affecting the other supply.

It's a dimes worth of protection for some much more expensive parts. A gamble. You may live a long time and never need the isolation. Then again, you don't really need a standby switch, do you? That amp has already survived 50+ years without one. Why does it need one now?

[g-man]

Deleted