Bias high voltage on HR Deville

[Bluebark]

Hi All, new to the forum and tube amps. Retired a few years back and decided to learn tube amps. I was basically gifted 2 non-functioning HR Deville amps and have attempted to repair the first one. The amp was a real mess. Case has suffered water damage and a couple of maybe hard hits (damaged corners). It powered on and I plugged in a guitar into the clean channel and it work. Scratchy pots and reverb worked. Hit the channel select and it started screaming so I shut it all down and tore it apart.

Once I got the boards out I saw a blown resistor (ate through first layer of glass) at R61. I continued on down the board and noticed the R80 & R81 were open. I did some digging and found this place. It seems like this has happened before and recommendations were to change out the 470’s for 1k or 1.5k 1W minimum resistors. I chose 1.2k 2W metals for R61 & R62. I replaced R80 & R81 with 100ohm 1W. At this point my OCD kicked in and I replaced all the fireproof carbon resistors out with metal film equivalent and raised the wattage a little. I applied the HR Deville tone/ground/input mods from the Formel website and did a full electrolytic cap refresh using F&T for filter caps and nichicon for all the rest. Looking over the board I found one cold joint so I reflowed all socket pins on the MB and anywhere else that looked fishy.

When I fired up the amp, everything worked. Didn’t sound too bad either. Went to check the bias at the pot and showed -51.1V. Hit the bias test point and it shows .728V. I have a basic tube tester and both tubes showed good but one is a little weak. Also, I can’t seem to find a schematic for Rev A boards so I am using Rev B specs. I know this is long winded but I felt knowing the history might help. Any advice at what might be causing the high voltage bias reading would be a great help.

Sovtek 6L6WXT

Pin      1            3        4          5         8
XV4   4.4mV   476V   473V   -51.3   .728V
XV5   2.1mV   475V   473V   -51.2   .729V

[AlNewman]

Are you sure you have your multimeter set properly?
For those voltages .0728V sounds more appropriate.
At .728 your tubes would be red plating.  Unless you, or someone else changed the 1R resistor to 10R?

[Bluebark]

Hi Al,
    And thank you for the fast reply. While checking the resistors at R61, R62 and R66 I found that one of the pads on R61 that goes to pin 4 had lifted of the MB, so I hardwired it. AND, like you said, I had a 100 ohm resistor sitting at R66 while spec is 1 ohm. That fixed the high voltage at bias test point. At least it was a stupid simple error on my ordering. OCD can be good in some aspects and bad in others...it's a constant battle. But when I consider this is my first amp fix and all the work I did to the MB with only one error, I am going say job well done.

Thank you once again. Sometimes all it takes is another perspective.

[Willabe]

.... I found that one of the pads on R61 that goes to pin 4 had lifted of the MB, so I hardwired it.

What's an MB?

[shooter]

mother-board??

[Bluebark]

LOL...sorry guys, computer jargon filtering into my post. So I guess CB (circuit board) would have been better. Hard to escape a world I lived in for 20+yrs.

[shooter]

 

Hard to escape a world I lived in for 20+yrs.

36 +
I started my detox program here, which lead to my current life as Amish 2.0!  we can have gas horses n limited WiFi 

[Bluebark]

Retirement is driving me crazy...more than I already am.

[shooter]

 


there are one 2 types of retired folks, ones that hate it, n ones that wondered why we didn't do this 40 years ago!!!


i'm in the 2nd camp!
 
the key is being able to self-start, once you get started, you look and it's noon, look again and it 8pm.  the garage has my snow-blower on blocks, being re-built from the ground up, the basement has the squirrel-cage blower out of furnace, ready for a good cleaning, on-deck the woodstove chimney clean, lawn to mow, trees to cut, my "to-do" list extends years past my future expiration date    


BONUS there is no boss wanting those "TPS reports"  (From the movie office space)