5E3 Testing and troubleshooting

[Mojojtm]

Hey All

Now that finally the Amp is up and running and adjusted few things such ground, (As per Martin advise on previous post) is time to test the Amp.
I am applying the same procedure used for 18 watts Amp

I turned the Amp on, the light lit, no smoke, (No Tubes plugged in) all seemed fine and at V1 I measured voltage between pins 4-5 and 9 and I read 6,76V AC, on the guide says it should read between 5-7V AC.

So I guess this is OK. Since I am always scared and I use super extreme caution I like always to be guided or have confirmation this is ok...

Next step would be testing the dangerous DC voltage high DC voltage that passes through the rectifier tube and the filter caps is referred to as “B+”

Now those next steps should be done at the 5Y3 basically the first Tube near the PT or power cord, I should plug in the Tube the 5Y3, and put in power cord, turn on the Amp (I usually use a wooden stick to touch any parts) at this point dangerous voltage is forming in the filter caps. If I understand the checks are done by Set your multimeter to 500V DC and connect the black (negative) probe to ground. Once that probe is secured to ground, measure the DC voltage at eyelet 27 (That is the eyelet with the filter cap This B+ voltage should be roughly 510V DC.

If that succeed should be all good to go put all the other tubes and switch on the Amp probably should work?

Thanks

[martin manning]

That all sounds good. You won't have any high voltage until you put the rectifier tube in, so that is another smoke test. Then you can put the output tubes in (make sure the speaker is connected). If that works, you should be safe from any catastrophic shorts. Many people will use an incandescent bulb in series with the AC input power to limit current for these first steps.

Beware that powering up with just the rectifier tube installed will charge the reservoir capacitor and all filters, and they will remain charged and dangerous since there is no path to discharge when you switch the power off. You should discharge the filters using a resistor before working inside the chassis. [edit: all filters are charged since there is no standby]

[Mojojtm]

That all sounds good. You won't have any high voltage until you put the rectifier tube in, so that is another smoke test. Then you can put the output tubes in (make sure the speaker is connected). If that works, you should be safe from any catastrophic shorts. Many people will use an incandescent bulb in series with the AC input power to limit current for these first steps.

Yes Light Bulb Current Limiter I have built one and is connected in between the amp the the wall outlet

[Mojojtm]

So I now plugged the 5Y3 switched on the Amp pilot light lit no issues the Tube also lit
No smoke black prob to ground, and with one hand I checked DC V on eyelet 27 I read 485V DC I read on the guide This B+ voltage should be roughly 510V DC.
I bet this is OK too?

[Mojojtm]

Actually a question that comes up in mind
The fact that Light Bulb Limiter is connected in between will this false the reading of DC Voltage?

[Phil_S]

Voltage will be low with the limiter in circuit. The main purpose of the bulb limiter is to detect a short that would damage the amp. As I understand it, you must use an incandescent bulb. These bulbs are getting harder to find.

If you have a 60W or higher rated bulb in the tester and it looks OK, you can remove the limiter. Then you will get a true voltage reading and it will be higher than what you reported to us.

[Mojojtm]

Voltage will be low with the limiter in circuit. The main purpose of the bulb limiter is to detect a short that would damage the amp. As I understand it, you must use an incandescent bulb. These bulbs are getting harder to find.

If you have a 60W or higher rated bulb in the tester and it looks OK, you can remove the limiter. Then you will get a true voltage reading and it will be higher than what you reported to us.

Actually the light bulb is 150W, let me re-test then

[Mojojtm]

Ok done!
I read without Light Bulb limiter 491V DC so little higher but not much of difference I'd say this is ok isn't?

[martin manning]

150W is high for this relatively low power amp. You won't see much reduction in voltage. A 40W would be safer, IMO.

[martin manning]

Ok done!
I read without Light Bulb limiter 491V DC so little higher but not much of difference I'd say this is ok isn't?

That's fine. You can install the rectifier with the limiter in and check voltages on all the filters.

[Mojojtm]

150W is high for this relatively low power amp. You won't see much reduction in voltage. A 40W would be safer, IMO.

Yes true but once I had a short on a 18 Watts Amp and I remember the light bulb light lit which was a good sign for a short that then I had to fix.

Anyway there seem to be no short as the Amp was on for 5 mins with 5Y3 on no smoke nothing unusual and Voltage measurement are close to what would be required so seems ok , so far so good no explosions lol

[Mojojtm]

Now one question that I should have asked earlier.
This kit came with 2x ECC83 or 12AX7

The guide is mentioning for the checks to look for the

Test the preamp tubes
If your readings so far are correct and the amp’s behaving normally, unplug it. With the amp unplugged, you can now install your 12AY7 and 12AX7 preamp tubes.

I only have 12AX7 2 times I read that in reality the difference is only about:

The most common reason for using a 12AY7 instead of the more common 12AX7 (ECC83) is that the 12AY7 has 45% of the gain of the 12AX7. So about half or 6dB in technical terms.

I bet is ok to use them both 12AX7 right?

[martin manning]

Sure, and you can compensate by turning the volume down. The additional gain will reduce the headroom as compared to a 12AY7.

I don't know why people like to install the preamp tubes first. IMO installing the power tubes will bring the voltages more into line, and the power stage is where errors or faulty components are likely to cause damage.

[Mojojtm]

Sure, and you can compensate by turning the volume down. The additional gain will reduce the headroom as compared to a 12AY7.

I don't know why people like to install the preamp tubes first. IMO installing the power tubes will bring the voltages more into line, and the power stage is where errors or faulty components are likely to cause damage.

I don't know why people like to install the preamp tubes, for me is because is written on the guide Stewmac or Mojotone so give it for granted that is the way it should be lol, I have read a lot in the last year but my experience is limited therefore I ask to the expert or people that are much more confident than myself

[martin manning]

A lot of things are just repeated from somewhere else, and these assembly guides are no different.