Search found 651 matches

by sonicmojo
Sat Dec 10, 2022 1:22 am
Forum: Technical Discussion
Topic: How much damage can I do?
Replies: 7
Views: 768

Re: How much damage can I do?

I don't yet have a 6973 to measure pins 3 and 6 but I have ordered a new set to see if it has any effect. At least with them I'll get the amp back to stock specs. Thanks!
by sonicmojo
Sat Dec 10, 2022 1:18 am
Forum: Technical Discussion
Topic: How much damage can I do?
Replies: 7
Views: 768

Re: How much damage can I do?

The data sheet for 6CZ5 says IC (internal connection) for pin 8. Maybe you can make some measurements to see if pin 8 goes to any other pins, but I usually take IC to mean "don't use this pin." Pin 8 on the 6CZ5 and 5CZ5 does not seem to have any connectivity to any other pins but 3 and 6 measure l...
by sonicmojo
Sat Dec 10, 2022 1:17 am
Forum: Technical Discussion
Topic: How much damage can I do?
Replies: 7
Views: 768

Re: How much damage can I do?

Also, if you look at the diagram for 6CZ5, grid 1 pins 3 & 6 are connected on the same side of the grid, but not on the 6973. I don't know if pin connections on same or different sides of a grid or any other component inside a tube make a difference or not. That is part of my question and any insigh...
by sonicmojo
Sat Dec 10, 2022 1:09 am
Forum: Technical Discussion
Topic: How much damage can I do?
Replies: 7
Views: 768

Re: How much damage can I do?

Running with a 20% overage they would probably not last long. Can you put a reversed pair of 1N4007's in each leg of the 6.3VAC feeding just those tubes? Hi Martin. Thanks for the feedback. I know it is a bad idea. I put them in for a minute and they work but got hot pretty fast. It is probably dif...
by sonicmojo
Fri Dec 09, 2022 10:48 pm
Forum: Technical Discussion
Topic: How much damage can I do?
Replies: 7
Views: 768

How much damage can I do?

Running 5V heater rated power tubes in a 6V heater circuit? I know I SHOULD PROBABLY NOT DO THIS but I have some 5CZ5 tubes that I want to run in place of some 6CZ5 tubes just to see how they sound in a Supro 1622RT (newer issue amp). As far as I can tell, these tubes are the same but different heat...
by sonicmojo
Fri Dec 09, 2022 10:39 pm
Forum: Speakers and Cabinets
Topic: EVM 12L dust filter repair
Replies: 1
Views: 2339

Re: EVM 12L dust filter repair

I say just pull it up with tweezers to straighten it out and run a little bit of glue around the edge to get it stuck back on there. I bought some micro mesh for some of my old JBLs but at least you still have the mesh.
by sonicmojo
Thu Sep 08, 2022 4:03 am
Forum: Technical Discussion
Topic: 250KA Presence Control - Mahalo
Replies: 8
Views: 930

Re: 250KA Presence Control - Mahalo

I appreciate all the ideas. I left the power section alone and incorporated some ideas from the Dirty Shirley details out there. It is Cathode follower before the tone stack. I used the extra triode on V2 that was available. It is mostly like a Dirty Shirley on the first 3 gain stages and the master...
by sonicmojo
Mon Sep 05, 2022 7:44 pm
Forum: Technical Discussion
Topic: 250KA Presence Control - Mahalo
Replies: 8
Views: 930

Re: 250KA Presence Control - Mahalo

Yes, cut control as seen on Vox AC15 and AC30. Do you have a schematic of this Mahalo amp? Thanks! I don't have a schematic. Swapping in output tubes capable of higher wattage output will buy you nothing with out a bigger transformer set! In fact bigger output tubes would just give you more clean h...
by sonicmojo
Mon Sep 05, 2022 9:48 am
Forum: Technical Discussion
Topic: 250KA Presence Control - Mahalo
Replies: 8
Views: 930

250KA Presence Control - Mahalo

Aloha, I recently acquired a Mahalo DR20 combo amp - made around 2014 (no Hawaii affiliation as far as I can tell). It has a 250KA presence control attached to the PI output with a simple .0047uF cap on the Presence pot. I was a bit confused by this design as I have never seen a Presence control imp...
by sonicmojo
Sun May 15, 2022 11:44 am
Forum: Fender Discussion
Topic: Fender Bandmaster hum.
Replies: 18
Views: 2616

Re: Fender Bandmaster hum.

You’ll definitely get hum with only one power tube installed. Have you tried a different pair of output tubes (hopefully closely matched) or do you have a bias probe to check the bias on each tube? Sounds a bit like mismatched output tubes to me but could be something else.
by sonicmojo
Sat May 07, 2022 2:12 am
Forum: Technical Discussion
Topic: uTracer (Micro Curve Tracer)
Replies: 284
Views: 79746

Re: uTracer (Micro Curve Tracer)

Darn it, with the price of tubes I am tempted to build my UT3+ kit that I bought in 2016 and do some real testing of the archives. Yikes, time flies! Glad to hear it is not obsolete!
by sonicmojo
Fri Apr 22, 2022 6:48 pm
Forum: Dumble Discussion
Topic: Help troubleshooting jm/an wonderland build
Replies: 5
Views: 901

Re: Help troubleshooting jm/an wonderland build

What is that loose wire under the filter cap board in pic#2? That might have been an earlier pic before you attached it but is the first thing I see.
by sonicmojo
Tue Oct 19, 2021 11:29 pm
Forum: Technical Discussion
Topic: Heat and electrolytic caps - proximity to power tubes an issue?
Replies: 8
Views: 962

Re: Heat and electrolytic caps - proximity to power tubes an issue?

The most common 40/20/20/20 CE can caps made today are only 55C/131F rated. I’ve seen many Princeton Reverbs fail with “not that old” new caps. Try to find caps with higher ratings.
by sonicmojo
Thu May 20, 2021 11:00 pm
Forum: Technical Discussion
Topic: Twin Reverb RI buzzy undertones
Replies: 9
Views: 1071

Re: Twin Reverb RI buzzy undertones

It appears on both channels. It is subtle so is very hard to tell if it is sympathetic vibrations but I'm convinced there is something going on. Unfortunately my scope has a mostly blown LCD so I am limited on what I can see and do). I need to get a new one. I just ran a signal generator through it ...
by sonicmojo
Thu May 20, 2021 9:25 pm
Forum: Technical Discussion
Topic: Twin Reverb RI buzzy undertones
Replies: 9
Views: 1071

Twin Reverb RI buzzy undertones

Aloha, I have a twin reverb in for repair as it just does not sound right. It has what seems to be a slight "coil" rub type sound where there is some slight fizzy buzzing in the background on notes no matter what cabinet used. This after the prior repairman and I have both gone through it pretty goo...