533 Build B+ C12 question..

[eideland]

Tweed Deluxe 5E3 build kit.

So I've got everything all wired as per Tube Depot's 5E3 build kit specs. My problem is when I get to checking voltage on the C12 (B+) for the rectifier tube I'm getting considerably more voltage then what is suggested. Recommendation from the build specs is +460V +/- 10v. I'm reading a steady 521V. Now granted, I purchased the actual Tweed Deluxe Power transformer from Magnetic Inc. (710V) instead of the Blackface Deluxe reverb Power transformer (660V) that comes with the kit.

Question is: Is the higher reading than normal strictly because of the difference in the power transformers? And will this harm my amp/tubes in anyway?

[Bruce / Mission Amps]

Tweed Deluxe 5E3 build kit.

So I've got everything all wired as per Tube Depot's 5E3 build kit specs. My problem is when I get to checking voltage on the C12 (B+) for the rectifier tube I'm getting considerably more voltage then what is suggested. Recommendation from the build specs is +460V +/- 10v. I'm reading a steady 521V. Now granted, I purchased the actual Tweed Deluxe Power transformer from Magnetic Inc. (710V) instead of the Blackface Deluxe reverb Power transformer (660V) that comes with the kit.

Question is: Is the higher reading than normal strictly because of the difference in the power transformers? And will this harm my amp/tubes in anyway?

What rectifier are you using and for that matter you can't do squat with DC voltage measurements until you put all the preamp and power tubes in to see how the PT windings and the B+ rail loads down.
Usually there is a higher B+ with the Deluxe Reverb PT although it is a great PT to use if you want to punch up the 5e3 and mess with the bias and the B+ rail to get closer to stock.

[eideland]

The rectifier tube is a Sovtek 5AR4. I haven't gone any further in my checks as I'm getting different readings. The build kit suggests testing everything in this order:

Step 8 – The panel indicator should illuminate. Visually verify that the filament inside the
rectifier tube is glowing. Monitor the amplifier for any unusual smoke or smells or blown fuse. If anything unusual occurs, disconnect power immediately and review connections. It is good practice to use a power strip with a circuit breaker and an on/off switch between the
wall power and the amplifier power cord as an improved electrical

Step 9 – With your multimeter on the 500 volt range, carefully
connect the meter's black lead to chassis ground (photo 8.1a)
and the red lead to the positive end of C12 (B+). The voltage
here should be something close to +460 +/- 10 volts (photo 8.1b).

Step 11 – Install both preamplifier tubes.

Step 12 – Plug the amplifier's AC power cord into the AC power source at the wall.

Step 13 - The panel indicator should illuminate. Monitor for any unusual smoke or smells or blown fuse. If anything unusual occurs, disconnect power immediately and review
connections.

Step 14 – Let the amplifier warm up for 2 minutes. With a multimeter on the
20 volt range, carefully connect the meter's black lead to chassis ground and
the red lead to the positive side of C3. The voltage here should be close to
+1.5 +/- .5 volts (photo 8.1c).

Step 15 – Move the red lead to the positive side of C6. The voltage here should be close to +1.5 +/- .5
volts (photo 8.1d).

Step 16 – Move the red meter lead to the lower lead of resistor R14. The voltage here should read +63V +/- 2.0V volts

Step 18 – Install the two power tubes.

Step 22 – The panel indicator should illuminate. Monitor for any unusual smoke or smells or blown fuse. If anything unusual occurs, disconnect power immediately and review
connections.

Step 23 – Let the amplifier warm for 2 minutes. With a multimeter on the 200 volt range, carefully connect the meter's black lead to chassis ground and the red lead to the positive side of C10. The voltage here should read close to +22 +/- 3 volts (photo 8.1e).

[Bruce / Mission Amps]

Well, even a NOS 5Y3GT with no load on it will charge the main filter caps to nearly peak ripple voltage, which in your amp will be:
710 / 2 = 355v x 1.4142 = 502vdc and if your line voltage is 117v-122v.
I'd hate to be those 450v to 500v filter caps though... make those tests quickly and at least get the preamp tubes in asap.

That 5AR4 is totally the wrong tube to be using after this though.
Get a NOS 5Y3GT or at the very least, a Sovtek 5Y3GT.

[eideland]

Thanks Bruce. Appreciate the help. After some more reading I think that will be a excellent idea. Saw you had replied to another thread at The Gear Page regarding someone changing their 5R4 for a 5Y3 and dropped their B+ from 340VDC to 318VDC. I also saw that a 5U4 could possibly drop the B+ another 10-20VDC less than the 5Y3. I'm not sure I want to go there though. Any thoughts on that?

[Bruce / Mission Amps]

Thanks Bruce. Appreciate the help. After some more reading I think that will be a excellent idea. Saw you had replied to another thread at The Gear Page regarding someone changing their 5R4 for a 5Y3 and dropped their B+ from 340VDC to 318VDC. I also saw that a 5U4 could possibly drop the B+ another 10-20VDC less than the 5Y3. I'm not sure I want to go there though. Any thoughts on that?

OK... just a thought.... don't get a 5AR4 mixed up with a 5R4, they are two different tubes.
I'm not sure about this ( I should be after this amount of time) but the 5U4 might not drop the B+ as far as the 5Y3GT in this amp.
It's a matter of how much load is on the rectifier and the tube's actual impedance... but a 5U4 is a real stout rectifier and the 5E3 drawing 65-75ma at idle might not load it down as much as you might think.
Actually, the best thing to do is look at the load charts for the rectifiers and you'll see how much V drop there is across the anodes to cathode(s) at different current levels and you'll get a better feel for this.
A 5R4 could drop the B+ down more but they have a lower filter capacitor tolerance so you have to be careful not to get carried away.
Using the 5E3's first 16uF cap with a 5R4 is probably OK in reality but adding a 47 to 68 ohm 5 watt resistor in series with the B+ leg from the rectifier tube socket to the first filter cap node will let you run just about any of those rectifiers with any first filter cap and not hurt the rectifier tube.
Then you can adjust the B+ with the rectifier set up.
And don't discount the simple dropping effect of the 5 watt 10-15v zener diodes in the high voltage center tap of the power tranny.

[eideland]

So I finally got the time to work on this amp some more. Went out n got the 5Y3GT tube for the rectifier. Voltage tests are much better for everything EXCEPT:

Step 16 – Move the red meter lead to the lower lead of resistor R14. The voltage here should read +63V +/- 2.0V volts

I'm reading 7.1V when I'm supposed to be getting 63V +/-2.0V Big difference? LOL This is a 1.5K 1/2W resistor on C section. I attached a image of the PCB.

I've double, triple and quadruple checked my wiring. I can't find ANYTHING that is mis-wired or bad. So I'm asking for any help. Thanks!

[loudthud]

I would suspect you are measuring at the bottom of R13 instead of R14 or you have miswired somehow. The point "m" won't measure properly because the meter will disrupt the circuit. The 63V should be at point "n" but I'd allow +/- 10V to account for variations in tubes.

[eideland]

Actually, I was measuring straight off of the R14 resistor, but I did try measuring at "n" as well. Still only getting 7.08V. "n" is wired up to pin 8 of the V2 preamp tube if that helps.

[loudthud]

Do you have the correct parts installed for R11 and R15 (56k) and a 12AX7 installed? You should be able to measure the resistance with the parts installed in the board as well as R13 and R14. Just be certain to discharge the filter caps before attempting to measure the resistance.

Check that you have a good solid connection to pins 4 and 5 of the tube socket. Remove the tube and examine the sockets where the tube plugs in for bent or damaged contacts. Look at the tube and verify that both sides have an equal glow from the filament.