Search found 13026 matches

by martin manning
Fri Mar 29, 2024 10:43 am
Forum: Dumble Discussion
Topic: Starting to populate the chassis....
Replies: 54
Views: 1582

Re: Starting to populate the chassis....

I see you have installed the filter and dropping resistor in the left rear corner of the chassis (as seen from the front) shown in the 124 layout. The main filter board you are using includes that filter. See the 183 layout for the B+4 and 5 connections that go with the board you are using.
by martin manning
Thu Mar 28, 2024 10:30 am
Forum: Marshall Discussion
Topic: 2204 build voltages are off
Replies: 9
Views: 256

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: 699

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: 699

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: 699

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: 266

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: 308

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: 6405

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: 256

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: 6405

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: 136

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: 456

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: 699

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: 699

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: 699

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...