single wire for heaters?

[allsavy]

My dinosaur of an amp has only one wire stringing all tube heaters in series. The center tap and the other wire are grounded. I'm currently working on other parts of the amp and can't hear it right now but when it was last running I thought the overall hum level was fairly low...not objectionable. This method seems easier to install. What is the diff between this and the standard twisted set? Any obvious benifit in tearing this out and going conventional?

[52 Bill]

My dinosaur of an amp has only one wire stringing all tube heaters in series. The center tap and the other wire are grounded.

Are they really in series?

[stingray_65]

I believe he means one tube after another
I've seen this too and wondered why it isnt used more often.

for example a single green wire running to pins 4 and 5 of a 12ax7 then to pin 7 on a 6v6

pins 9 and 2 respectivley grounded

I saw this on a Princtonesque SE with very little hum even for a single ended amp

[jrfrond]

If your tube numbers begin with "6" or "12", then you have a grounded heater string. If they are odd numbers like "5", "35", "50", etc., then you have an OLD amp with a line-operated series-heater string. You need to know this first.

[allsavy]

The tubes are 12 and 6. One heater wire running to each tube in a string as described above.

[Enzo]

Do you understand that is still a parallel wiring plan, not series?

[allsavy]

Parallel... yeah I get that.

[jrfrond]

The tubes are 12 and 6. One heater wire running to each tube in a string as described above.

Yep, a parallel heater string with one side grounded. If it works fine, leave it alone.

[Rick Erickson]

[What is the diff between this and the standard twisted set? Any obvious benifit in tearing this out and going conventional?]

The difference is your heaters are wired unbalanced and the twisted arrangement is usually balanced. Picture it as the difference between a single coil pickup and a humbucker. If you don't turn up the volume of your amp there won't be a very noticable difference in the hum level between these two types of guitar pickups. But in a high gain situation the Humbucker will have far less hum. In an amplifier, if it is a low gain type amp you can get away with the unbalanced heater arrangement and most people won't mind. In a single ended amp there is probably more hum coming from the power tube than the heaters anyway. The old JMI Vox aC 30 amps had unbalanced heaters, even though they had twisted wires running to the tubes. Clipping the ground jumper and installing balancing resistors makes a very noticable difference in these amps. As for yours - if it doesn't bother you, why change it?

RE