300b's for Kaiju

[drewh1]

Thanks Doc and Paul - I am definitely taking this one slow and will be careful about the voltages through every step. When I get to putting the tubes in, I'll take all the measurements and check in with you Paul about any needed changes.

yeah, it would be great if I had a crap pair of 300b's to test with, like most of us, I am extravagant in some ways and really cheap in others.  The kit looks great and I am really excited to be building it.

drew.

[drewh1]

So I just did the transformer power tests.  My house circuit is right at 125. I wired it accordingly.

7 &8 -  199.7
11 & 14 -  6.74
12 & 13 - 6.74

I am a bit over the 5% on all of these.  Just checkin, let me know if I should change something.


drew.

[Paul Joppa]

That is a bit on the high side. It will drop a bit when the transformer is drawing full current, but probably not enough.

However, the EML mesh 300B draws 1.4 amps, greater than the 300B spec of 1.2 amps. This will pull the filament voltage down further than normal.

If you are lucky, these two effects will cancel each other. So I suggest you proceed with the stock build, and add an AC voltage measurement across the filament (socket pins 1 and 4) before proceeding with the other voltage measurements. If you still have a voltage outside the EML spec of 4.8 to 5.2vRMS, you can adjust the 0.51 ohm resistors to refine it. (See these resistors in the photo on page 35 of the manual.)

Incidentally, you may wish to mark the setting of the hum pot before installing the DC heater circuit. It will otherwise be difficult to determine the best setting.

[drewh1]

Great minds think alike!  I was wondering if the additional voltage would bring it closer to spec.

BTW, I did manage to get my hands on a pair of 300bs to set up and test with, so I am good to go. I'll just keep checking in with details as things move along.

I really appreciate all your time and help Paul, but what are you doing working on a Saturday!

drew.