Pretty nice work for a Surf Bum.....
Because I have minimal computer skills, I am equally impressed with your lay-out and that kind of "stuff'. The build quality, of course, is also a joy to look at.
Hope you do not mind if I save that lay-out for a future build.
Thank You
hh, no problemo dude! Okay so I "bulbed" it with my new bulblimiter...the VVR was weird, seemed like when I turned it up, the Vs went down. The Vs were also all low I assumed it was due to the 25w bulb. So it ran for a while, the 1k5Ws didn't fry with all tubes in and everything dimed. Checked all the main voltages, etc. Probed around, everything seemed cool. So then I plugged straight into wall. Zero hum btw. That's good. probed around a bit. Some hissing with it dimed, somewhat minimal for using no shielded runs - I expected worse. No oscillation (with just speaker plugged in). Had it on for well over a minute or two. Started probing. V before the 1k5W (342VAC which is high still). V after the diodes (392VDC). Started to write it down, probed the PT secondaries again to verify the 342 and musta touched something cuz I heard a hum, then nothing. Got worried. No smoke. Rs are fine. The fuse blew.
Kid sleeping, more fuses buried deep in a box in the back of the kid's closet. Tomorrow...
Any idea why I'm getting 342 and not 300 out of the PT? I had all the tubes in. Also any idea why the fuse blew?
Were you monitoring any AC current when you were testing? Did you replace the FET in your VVR since the incident when you powered it up w/o the insulator?
Bypass the VVR, re-fuse and fire her up w/ the bulb limiter.
I did not check AC current. I did install a new NTE mosfet. The VVR was scaling voltage as I turned the pot. The fuse blew while I was re-measuring the PT secondary voltage. I was not turning any pots or anything for prob 30 seconds to a minute, so it was stable at the time. Just started to DMM stuff when it happened but the amp was on for a bit.
surfsup wrote:I did not check AC current. I did install a new NTE mosfet. The VVR was scaling voltage as I turned the pot. The fuse blew while I was re-measuring the PT secondary voltage. I was not turning any pots or anything for prob 30 seconds to a minute, so it was stable at the time. Just started to DMM stuff when it happened but the amp was on for a bit.
Hopefully you accidentally bumped something with a test lead and it's not a problem with the amp.
With my experience using a bulb limiter, you have plenty of time to shut down before any fuses blow. I don't get that same amount of time when using a variac alone.
Re: the fuse...because I was wondering about this, I found an old post by tubeswell, here is the summary:
The AC fuse value is calculated using VoltAmps (VA). The total VA used is the summary of the secondary VA of the PT. Example for PT with 300-0-300, 150mA w.6.3V@4A heater winding
300*0.15=45
6.3*4=25.2
70.2 VA total for PT secondaries
VA/Vmains = Amps
70.2/125.2V = 0.56A fuse but it is good practice to double this value
0.56 * 2 = 1.15A fuse so the 1A fuse seems to be a good value to use, my only concern is if I should be using 300V or 600V as my voltage for the first calculation.