Search found 405 matches

by pula58
Mon Jan 01, 2018 3:43 am
Forum: Technical Discussion
Topic: Holland Amp
Replies: 38
Views: 5606

Re: Holland Amp

I worked on a Holland "Lil Jimi" several years ago. The pots weren't making good contact with the oxidized aluminum chassis! Same as you! So I roughed -up the metal and applied some non-ox pastes. What a difference it made!
by pula58
Sat Dec 16, 2017 10:11 pm
Forum: Dumble Discussion
Topic: Why Dumble cleans?
Replies: 26
Views: 5124

Why Dumble cleans?

Hi Folks, I am so comfortable with Fender Blackface style clean tones, have built them, and used them for years. For those of you you who like Dumble-style clean tones (i.e., amp overdrive not engaged), I would be very curious to hear which of the architectures of which you enjoy the clean tone, and...
by pula58
Wed Jun 22, 2016 8:00 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

Re: When a power-tube screen "shorts"....

A fuse is a better defined protection device - use a fast blow fuse (as there is no normal in-rush or short-duration high current condition above max tube current draw). Adding a 150V 5W zener across the fuse is an additional measure that can save the tube when the fuse has blown for other reasons ...
by pula58
Wed Jun 22, 2016 7:45 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

Re: When a power-tube screen "shorts"....

A fuse is a better defined protection device - use a fast blow fuse (as there is no normal in-rush or short-duration high current condition above max tube current draw). Adding a 150V 5W zener across the fuse is an additional measure that can save the tube when the fuse has blown for other reasons ...
by pula58
Mon Jun 20, 2016 11:44 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

Re: When a power-tube screen "shorts"....

labb wrote:The Crate Blue Voodoo fuses the cathode. Take a look a BV-60 schematic for the power tubes
Ah...indeed it does...thanks P.
by pula58
Mon Jun 20, 2016 7:28 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

Re: When a power-tube screen "shorts"....

Signal grid and suppressor grid* first, then cathode (but could be plate as well, although that is not likely to cause meltdown), depending on how the screen grid (and the screen grid support rods) start to melt and flex inside the electrode cage. * or beam plate (in a tetrode) Seems like a cathode...
by pula58
Mon Jun 20, 2016 5:08 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

Re: When a power-tube screen "shorts"....

Hi Steve, thanks for your input.
I guess what I am trying to first understand is exactly what happens when there is a screen short. Where is the screen shorting-to?

I like the idea of cathode fuses since the voltages are low there.
by pula58
Mon Jun 20, 2016 4:57 pm
Forum: Technical Discussion
Topic: When a power-tube screen "shorts"....
Replies: 15
Views: 1779

When a power-tube screen "shorts"....

Is the screen grid shorting to the cathode? Seems like it must be. If it was shorting to the grid, then the grid leakage resistors are large enough in value to limit the current to a degree that the screen grid resistors would not fry. So then, my feeling is that fusing in between the power tube cat...
by pula58
Tue Jun 07, 2016 1:28 pm
Forum: Technical Discussion
Topic: Coax (shielded) cable
Replies: 19
Views: 4357

Re: Coax (shielded) cable

the inner conductor of this coax is way thinner than 22 AWG. I am concerned about reliability in terms of mechanical reliability, not current limits.
by pula58
Mon Jun 06, 2016 1:16 pm
Forum: Technical Discussion
Topic: Coax (shielded) cable
Replies: 19
Views: 4357

Re: Coax (shielded) cable

the inner conductor of this coax is way thinner than 22 AWG. I am concerned about reliability in terms of mechanical reliability, not current limits.
by pula58
Sun Jun 05, 2016 10:56 pm
Forum: Technical Discussion
Topic: Coax (shielded) cable
Replies: 19
Views: 4357

Coax (shielded) cable

I have a batch of RG 187...the inner conductor is SO thin...makes me worried about long term reliability. What are you folks using for Coax that has a reasonably low capacitance per foot, but also has an inner conductor that is robust. I had some RG 187 from Apex Jr..loved it.. Then I got another ba...
by pula58
Sun Mar 15, 2015 3:43 am
Forum: Technical Discussion
Topic: 4x6V6 output transformer
Replies: 67
Views: 11087

Re: 4x6V6 output transformer

Mercury magnetics makes a clone of an old Jim Kelley 4x6V6 OT.
I think it's called the: JIMK-O

The amp I played it in was a Fargen Blackface style amplifier and I thought it sounded very good.

good luck!

P.
by pula58
Mon Feb 23, 2015 4:46 pm
Forum: Technical Discussion
Topic: Marshall JCM2000 (100W)- heater circuit failure
Replies: 3
Views: 776

Re: Marshall JCM2000 (100W)- heater circuit failure

Yep, 2K resistance solder joint to one sockets pin-7

:-)
by pula58
Mon Feb 23, 2015 5:14 am
Forum: Technical Discussion
Topic: Marshall JCM2000 (100W)- heater circuit failure
Replies: 3
Views: 776

Marshall JCM2000 (100W)- heater circuit failure

Customer brought his 100W JCM 2000 into the shop. One of the power tubes isn't heating. I swap tubes, the problem stays with the one socket of interest ( "V6"). I take out the tube from that socket, stick my multimeter probes into pins 2 and 7 of the socket and measure 7V RMS AC. Looks about right. ...