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by martin manning
Thu Mar 28, 2024 10:30 am
Forum: Marshall Discussion
Topic: 2204 build voltages are off
Replies: 9
Views: 214

Re: 2204 build voltages are off

Why are you going around measuring voltages without all the tubes installed ? You won't get any accurate measurements, that mean anything, that way I think no-load voltage at the reservoir is a good piece of information when starting up a new build, and it's the first thing I look at, usually long ...
by martin manning
Wed Mar 27, 2024 1:03 am
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

Wow, time flies! I think 'll stick with 6V6. You're right EL84 has very low drive voltage requirement.
by martin manning
Tue Mar 26, 2024 8:55 pm
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

rogb wrote: Tue Mar 26, 2024 8:17 pmI did on my EF86 SE, and 6L6
Thanks, Rog. So EL84 was your preference over 6V6? Was it a close call? I could be persuaded to switch, if that's the hands-down best tone. Planning for 6V6, my plate voltage is going to be quite a bit higher than Matt used, however. What primary impedance did you use?
by martin manning
Tue Mar 26, 2024 4:57 pm
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

10thTx wrote: Tue Mar 26, 2024 12:38 am...tried building his SE amp using 6L6's. It didn't come close to the tone Mat got using EL84's.
Anybody try using 6V6?
by martin manning
Tue Mar 26, 2024 4:26 pm
Forum: Dumble Discussion
Topic: Signal resistor type
Replies: 6
Views: 254

Re: Signal resistor type

I smell them. KOA's smell strongly of crushed gravel, where the Dale's have a volcanic ash note ;^)
by martin manning
Tue Mar 26, 2024 2:50 pm
Forum: Dumble Discussion
Topic: Bluesmaster HRM question:
Replies: 10
Views: 297

Re: Bluesmaster HRM question:

Taper is about where in the rotation you get a given percentage of resistance, and also describes the change in percentage per degree along the way, which makes a significant difference in the usability of the control. An extreme case would be a linear volume pot, which results in a high volume leve...
by martin manning
Tue Mar 26, 2024 11:53 am
Forum: Dumble Discussion
Topic: 3rd Gen started
Replies: 82
Views: 6395

Re: 3rd Gen started

All good questions. Recent production does not even have the outer foil bar on the label.
by martin manning
Tue Mar 26, 2024 11:14 am
Forum: Marshall Discussion
Topic: 2204 build voltages are off
Replies: 9
Views: 214

Re: 2204 build voltages are off

lgehrig4 wrote: Mon Mar 25, 2024 6:43 pmLooking good now! The only questionable reading it V2 pin6 (336), which is approximately 80 higher than the chart. Should I be concerned about this?
That appears to be an error in the voltage table you linked. It should be ~350, same as the B+4 node voltage.
by martin manning
Tue Mar 26, 2024 10:48 am
Forum: Dumble Discussion
Topic: 3rd Gen started
Replies: 82
Views: 6395

Re: 3rd Gen started

In the photos, is the orientation indicated by a mark added by the builder, or a factory label, which is likely to be random in orientation?
by martin manning
Tue Mar 26, 2024 10:45 am
Forum: Technical Discussion
Topic: Knight 600 valve emissions tester thoughts?
Replies: 5
Views: 121

Re: Knight 600 valve emissions tester thoughts?

Stevem wrote: Tue Mar 26, 2024 10:07 amThese type of testers can not even tell you if a tube is gassy which will ultimately shorten its life.
This tester does do a gas test, which I believe on these types of testers looks for excessive grid current.
by martin manning
Tue Mar 26, 2024 10:32 am
Forum: Technical Discussion
Topic: Flash seen from bottom of 12AT7 PI socket
Replies: 22
Views: 380

Re: Flash seen from bottom of 12AT7 PI socket

pjd3 wrote: Mon Mar 18, 2024 7:52 pm...I witnessed a whiteish flash through the base of the Phase inverter socket that had a NOS 12AT7 in it. I have not seen this happen before and it alarmed me.
Heater flash from video linked by Mark in Knight emissions tester post: https://youtu.be/SMHS1DNS8FA?t=169
by martin manning
Mon Mar 25, 2024 8:44 pm
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

No problem, it's all good input! Sounds good, too. Interesting you had success with a 6L6, what with its need for more drive voltage than an EL84 or 6V6.
by martin manning
Mon Mar 25, 2024 7:45 pm
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

Excellent! I had forgotten all about that. I have the schematic Colossal drew up, which has some good ideas. Matt drives an EL84 directly, where I'm planning on a 6V6. I want to ditch the preamp out/power amp in, and take a line out from the output transformer. That will be driving either a resistiv...
by martin manning
Mon Mar 25, 2024 10:23 am
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

The 20/20 must be pretty crowded inside, maybe a bit hard to work on? My project is a single ended amp, so no PI. I don't know if I'll miss it since the Dumble power amp is pretty much a clean Hi-Fi type. It's a bit of an experiment, so I'll just have to see how it turns out. The preamp is a copy of...
by martin manning
Sun Mar 24, 2024 9:22 pm
Forum: Dumble Discussion
Topic: New Project
Replies: 26
Views: 663

Re: New Project

pullshocks wrote: Sun Mar 24, 2024 8:49 pmSingle ended amp?
Yes! With built-in resistive load and pseudo-balanced line out.