Recent Posts

51

Effects / Re: Safety / Filtering Capacitors across the Primary on mains powered effects

« Last post by sluckey on June 08, 2026, 05:17:20 pm »

I would replace it with a Class X cap.

52

Effects / Safety / Filtering Capacitors across the Primary on mains powered effects

« Last post by Rontone on June 08, 2026, 04:39:26 pm »

I've just done a recap on a tape echo, the last cap is one of those put across the live and neutral on the primary side after the switch, typically a 0.05uF 630V on old units,

I was thinking of just snipping it off, but wonder how bad it could be as reading some threads online it seems they do help with motor units as well as filtering

Its been put in a really awkward place too!

53

Tube Amp Building - Tweaks - Repairs / Re: First amp build

« Last post by Mongrel714 on June 08, 2026, 03:46:01 pm »

I'm not crazy about the bias power supply switching off with the Standby switch.

Yeah, and the fusing on the Secondary HT can be better, have a look at some standby and fusing ideas here:-

https://www.valvewizard.co.uk/standby.html

https://www.valvewizard.co.uk/fuses.html

That makes sense, I wondered why my current amp had a couple fuses inside, now I know, still a little confused as to the location of the fuse to protect the PT, I'll re read that a few times till it sinks in my thick skull, I remember nights on the road and blowing a fuse in my Plexi, "give me some aluminum foil!!" Sometimes it would get me through the night, other times It didn't!! Anyways, thanks guys! Keep the knowledge coming!

54

Tube Amp Building - Tweaks - Repairs / Re: Bias Help for Rob Robinette JCM800 6V6

« Last post by sluckey on June 08, 2026, 10:02:43 am »

Thanks again @sluckey. Quick question on the resistor values.
I noticed you have a 47k going to ground, is that particular to your circuit?
Ill be leaving my 220k resistors on the grid leaks.

yes

Should I leave the 2x 10K resistors going from the POT to the DIOD and ground the POT as per the original diagram?
In other words, just leave it as is but omitting the 50k micro trimmer?

No! Wire the circuit as shown, either exactly as shown in my drawing or exactly as shown in Rob's drawing. Choose one circuit or the other. Do not deviate. The bias circuit is too critical to the life of your output tubes to monkey around.

Should my total resistance going from the 220k Grid Leaks to ground be at approximately 75k?

Which circuit? In my circuit the resistance can be as high as 72K or as low as 47K, depending on the setting of the single pot. In Rob's circuit the resistance can be as high as 82.5K or as low as 7.5K.

55

Other Topics / Re: Meme of the day

« Last post by shooter on June 08, 2026, 10:00:07 am »

....

56

Tube Amp Building - Tweaks - Repairs / Re: First amp build

« Last post by JPK on June 08, 2026, 08:01:53 am »

Bias switching off with standby, does that mean the tubes are un biased when the standby is on? What effect does this have?

See post #13.
https://el34world.com/Forum/index.php?topic=23011.0

57

Tube Amp Building - Tweaks - Repairs / Re: Tube Preamp SMPS

« Last post by DummyLoad on June 08, 2026, 03:08:09 am »

Tamed it with a with a pair of Pi filters - The first iteration I used a single 20H 10uF Pi filter, was ok, but still had some pop/buzz - Added a second Pi filter with 100uH 4.7uF, fixed most of the noise. Not perfect but tolerable and usable. Has about 23-30mV of ripple now, down from about 150mV average. I wound the toroid myself - Had some ferrite cores from a lab that was shutdown, so wound a  Micrometals T68-3 with 25 turns of 24AWG, salvaged and stripped wire from an old ethernet cable. No, you don't need 1W Rs in HV string, that's what I had in the bins. 

Schema attached.

Pic of ripple measurement of B+ line - Link below.

https://www.dropbox.com/scl/fi/z9kjf10i7owtmwhq1g5ot/IMG_20260608_021259634_HDR.jpg?rlkey=xgynz75541ry58kwv7kcrz7vc&st=fjdakbg0&dl=0

--Pete

EDIT: The 1W resistors in my application are overkill, my circuit draws about 3mA total. YMMV - Depends on the PS current load.

58

Tube Amp Building - Tweaks - Repairs / Re: Bias Help for Rob Robinette JCM800 6V6

« Last post by rud85ny on June 08, 2026, 02:28:06 am »

Should my total resistance going from the 220k Grid Leaks to ground be at approximately 75k?

59

Tube Amp Building - Tweaks - Repairs / Re: Bias Help for Rob Robinette JCM800 6V6

« Last post by rud85ny on June 08, 2026, 02:22:41 am »

Thanks again @sluckey. Quick question on the resistor values.
I noticed you have a 47k going to ground, is that particular to your circuit?
Ill be leaving my 220k resistors on the grid leaks.

Should I leave the 2x 10K resistors going from the POT to the DIOD and ground the POT as per the original diagram?
In other words, just leave it as is but omitting the 50k micro trimmer?

60

Tube Amp Building - Tweaks - Repairs / Re: First amp build

« Last post by Mongrel714 on June 07, 2026, 09:50:24 pm »

Bias switching off with standby, does that mean the tubes are un biased when the standby is on? What effect does this have?