New PCB Express build - seeking advice

[rock_mumbles]

... you could install your resistors there and then when the amp is turned off, flip the standby swith to play position to bleed the rest of the power supply circuit ...

RJ thought this one through with the PCB design. By having a bleeder on both sides of the standby (if you're sticking to the Express schematic for the placement of the standby), the entire rail drains after shutdown with no further action required by the player. That's great design and an improvement in safety.

I agree!

[Koop]

Next question...another case where the photos and schematic have me second guessing. The 1 ohm resistor for bias checking is shown on pin 8 (cathode) in the schematic but in the pictures it looks like everyone is tying pin 1 (grid 3) to pin 8. Pin 8 is what I used in previous builds (6V6 power tubes). Should I tie the two pins?

[rock_mumbles]

[img:470:279]http://www.justinholton.com/hotrod/imag ... basing.gif[/img]
Compare the two pictures look at pin 1 on the EL34 (Suppressor grid) look for a similar component in the 6L6 ... it's connected to pin 8

The suppressor grid can be either connected to ground or to the cathode, the cathode is really close by ...

[Koop]

Thanks rock. Great way to explain it. The visual always helps.

[Koop]

I finished wiring it up and just made the last solder joints at pin 3 of V4 & V5. You guys are the greatest, I couldn't have done it without the resources and guidance available on this forum.

Before I pat myself on the back, I'm going to kick back, sip a glass of wine and look things over. Tomorrow I'll look it over again with fresh eyes and begin the initial start up. I'm confident it'll work - as Kevin Cameron says "it doesn't have any choice if you built it right".

Thanks again for all the help - especially Mark Fowler, Colossal, rock_mumbles and the OP mattvon. Following the death of my mother a few weeks ago, getting back into this has been good therapy.

[dorrisant]

Koop,
Sorry about your loss... good luck with the startup!

Tony

[M Fowler]

Koop so sorry for the loss of your mother.

The startup will go smooth I'm counting on you and yes this is good therapy.

Mark

[Koop]

Thanks guys - the start up was fine, best amp I've ever played. I posted a thread titled "Over the Moon".

[rock_mumbles]

Sorry to hear about your mother ...

[RJ Guitars]

I don't think I ever said thanks to you guys for building this amp and running this post. I was overwhelmed at that time with personal issues and I missed most of this post... thanks guys for your work. Now I gotta look up that "Over the moon" post rj

[mattvon]

Hey all...after nearly two years, I've returned to finish this amp! For a number of reasons (none amp related ) I haven't been able to get to a place I could wrap this up.

To pick up where I left off, I've gotten all of the components wired up and have done the "no tubes, light bulb limiter" power up and hooray! No smoke! The light bulb brightens, then dims right away as it should. My voltage values appear to be ok (a bit low, but I understand that's likely due to the current limiter).

I have also given it the power up test with tubes installed: not as good. With all the tubes in place, the light bulb stays bright--I shut it down right away.

Pull the power tubes and it brightens, then dims as it should--I'm thinking this means the noval tubes are wired correctly?

I've tried a couple of sets of power tubes, same behavior. I'm wondering if I've mis-wired my octal sockets.

Does anyone have a picture of a PCB Express build showing the power tube sockets they'd be willing to share? Or any ideas what to check for? I PM'ed rj, but I'm guessing he's too busy playing his Express to check the forum any more.

Thanks in advance for any help!

[mattvon]

Sorry, double-post.

[martin manning]

Where have you got the bias set? Initially it should be adjusted so that the voltage on pins 5 of the power tubes is at the lowest (most negative) value.

A good picture of the board wiring is here: https://tubeamparchive.com/viewtopic.ph ... 729#201729

[mattvon]

Thanks for the link to that picture! That's very helpful...I have a somewhat different version of PCB, but I think I'm following it. Here's where I'm different than the picture:

I don't have the pair of black resistors shown from pin 1 (or eight) to ground. Are those 1 ohm 2 watt resistors? It's a bit hard to tell from the picture.

I followed the layout in the build guide, so I have a plain jumper to ground from pin 1 (and pin eight).

I also am not using the chain of diodes, but I don't believe that's contributing to the issue.

I followed the start up procedure in the build guide and have the bias at it's midway point.

[martin manning]

Not sure about the wattage of those black resistors, but they are 1R. I would want to install those to make it easier to set the bias. What is the wattage of the bulb in your limiter, and how bright is it when the tubes are in?