Hot Rod Deluxe Hum

[tmlesko]

My HR Deluxe has a noticeable hum, independent of volume level. I don't have much for test equipment, just a meter. Is there anything I can check? I have tried different outlets in the house, same hum. I don't have a filtered power supply. I just got this amp and had to replace the reverb tank, with the help of forum members. It had the hum with the old tank too. Any thoughts?

Thanks in advance.
Tom L.

[Enzo]

Cracked solder on the power tube sockets. Cracked solder on a filter cap. Open screen resistor on a tube. shorted power tube. seriously mismatched power tubes. Seriously off bias adjustment

[tmlesko]

Thanks Enzo, I will give the pc board a visual inspection, if I can't find anything you mentioned, sounds like I need to take it to an experienced tech.

Tom L.

[tmlesko]

Enzo,
When you say "cracked" solder joint do mean "cold" solder joint?

Tom L.

[Enzo]

I mean there is a physical crack in the solder.

Look closely at any solder joint. SOmething sticks up through a hole in the circuit board. There should be a little volcano shape of solder curving smoothly up from the copper trace on the board to the sides of the wire poking through.

Now imagine that something is a leg from the tube socket, and due to thermal expansion/contraction and vibration, the solder has let go from the pin. There will be actual physical cracks in the solder - visible cracks.

Same sort of thing happens to jacks and controls, filter caps and power resistors.

[tmlesko]

Thanks, yet again, I got the picture. Guess I never saw a cracked solder joint, just cold ones, but I only worked as an electronics tech for 3 years.

I am noticing that the hum is progressively worse as the amp warms up and it seems to be slightly louder today than yesterday. I did get a filtered power strip, no difference.

I am looking at tube testers since I now have several tube amps and radios.

Tom L.

[tubeswell]

There's alot of testing you can do without fancy gizmos. Pop some fresh tubes in and see if the hum goes. (you're going to need new tubes eventually anyway - why not have a set on standby?) If the hum is still there, then you know you got to look somehwhere else

[tmlesko]

Can you recommend a source for tubes?

Thanks,

Tom L.

[tubeswell]

Sorry my sources are a several thousand miles away from you, and I don't think that would be practical

But under google just now I saw

www.vacuumtubes.com

www.tubesandmore.com

www.tubeworld.com

www.vacuumtubesinc.com

www.vacuumtubes.net

No idea what they are like

[Enzo]

Others I have never used are Tube Depot, DOug's Tubes.

Tubesandmore.com is a straightup place. I do business with their wholesale division.

Bob at Eurotubes.com will treat you right, but he only sells JJ tubes. JJs are fine, but if you prefer SOvteks, he ain't the guy.


Here, go to this link, and scroll down to the first photos and look at upper left one C2. Classic cracked solder, just as seen on tube sockets.

http://www.espec.de/uploads/media/Micro_Crack.pdf

[tmlesko]

You guys are a great help, thanks!

Tom L.

[tmlesko]

JJs are fine, but if you prefer SOvteks, he ain't the guy.

I'm afraid I don't know the various audio/tonal qualities of the tubes available today. My electronics training was 40 years ago and the tubes were military; Raytheon, etc. and we only cared about voice and signal transmission.

From one of "Tubeswell's" posts elsewhere, I see, "RCA, Mullard, Telefunken, Tung-Sol, Sylvania, Siemens, Phillips, GE, Tesla, Raytheon, Brimar" as NOS brands and "Electroharmonix, JJ, & Sovtek as re-issues." I prefer soft mellow sounds these days so is there a particular brand that is favored for that? Should they all be matched? Are the tubes matched to each other or just matched sections of the same tube?

On the Fender Forum I believe, I read that some prefer to change out the volume pot for audio taper type for a more evenly distributed range. Would this be advisable? I don't seem to have the stock volume over 2 when I play.

Tom L.

[tubeswell]

EH, Sovtek and JJ all do current production versions of popular guitar amp tubes. They are made in different factories, Sovtek is the Reflektor plant in Russia, JJ one of the old the old Tesla plants in Slovakia, and EH I'm not sure. New Sensor Corp market a bunch of 're-issue' tubes, some of which are alright, like their RI 'Tung-Sol" 6V6GT, which can take higher voltages and sound lovely and mellow. JJ 6V6s can take about the highest voltages in any 6V6, new or old but they're not as mellow as the new sensor "Tung-Sol" RIs - JM2CW

NOS tubes are what they are. RCA black plates are good 6V6s. Of the pre-amp tubes, pretty much any of those brands you mentioned would be nice (assuming you don't land with a dud), but they all sound different and have their own characteristics. You never know what a tube is going to give you in a particular amp until you plug it in (its like Forest Gump's mum's proverbial box of chocolates).

EH do a really nice modern production 12AY7. A fat creamy sound.

FWIW so you can get an idea - I have attached a recent .mp3 of one of my amps (5G9) (dry mix) with EH 12AY7 in V1, and New Sensor Tung-Sol RI 6V6GTs (through a G12M) The bright channel volume was on about 2.5/10 and tone control was at mid-point hence its quite clean and mellow - I just realised there is a chord mistake in the 2nd verse on the backing track (I played a B when it was meant to be a D7 - ooops)

[tmlesko]

Your "Stardust" was nice, thanks.

I am an architecture professor now and I REALLY appreciate the (re)education you guys are giving me! Thanks!

I just saw some Phillips JAN 7581A's on Ebay . . .$199 for a matched pair - WOW! (As I recall, JAN meant Joint Army Navy back then, suppose it still does) Should have collected tubes back in the day!

Tom L.

[tmlesko]

Hum Greatly Reduced!

Well, I looked over the pc board where the tubes are mounted for cracked solder etc. I could not see anything bad looking. All the joints looked shiny and in tack. I checked the grounds on the reverb tank and *then* I decided to swap the locations of the two 12AX7 pre-amp tubes and the hum got noticeably quieter! The hum is not gone, but is much quieter, on a 0-10 scale it went from a 5 to a 2. So, might I assume that a new set of tubes would make the difference? I noticed a 1996 date on the PC board and Made in USA on the tube ID sheet inside the case.

TL