Fender Hot Rod Deluxe - problem after tubes replacement

[pmdez]

Hi all!

I'm an (not very happy) owner of Fender HRDx. Few days ago I've replaced stock tubes with JJ's. I've found interesting post about replacing 12ax7's with something different and decided to give it a try.
Power tubes are 6L6-GC (biased around 70-71mV),
preamp:
v1 - ECC81 (12AT7)
v2 - ECC832 (12DW7)
v3 - ECC83-S (12AX7)

My amp version is probably II, Made in Mexico, produced circa 2008 - 2009.

The problem is that when I'm turning amp on from cold it starts to make strange noise, I don't know how to describe it, I'm not a native english. It's constantly crackling like car engine, one huge buzz. When I turn amp off and on again problem disappears.

Thank you in advance for help.

[Jana]

Does the problem go away if you put 12AX7 tubes in the preamp? The only tube substitutions I would do in this amp is to try a 12AY7 in V1.

[Stevem]

The power transformer in those amps where not made to handle feeding that much current to the output tubes.
If you have not harmed it yet, you will with that 70 ma on each tube.
With the plate voltage these amps have I find 45 ma to be the max that sounds good.

[Jana]

If you look at the schematic, the HRDX has the cathodes for the power tubes tied together and there is one bias test point that is the sum of the current for both tubes.

[pmdez]

If you look at the schematic, the HRDX has the cathodes for the power tubes tied together and there is one bias test point that is the sum of the current for both tubes.

Exactly, 70mV is a sum for both power tubes.

Does the problem go away if you put 12AX7 tubes in the preamp? The only tube substitutions I would do in this amp is to try a 12AY7 in V1.

The only reason that I've put this particular set of preamp tubes is that someone already tried it get better sound - less gain, bit more dynamics and headroom on lower volumes. And indeed it does sound better for my ears.

I will try to swap the tubes for 12AX7 and check if it resolve the problem. Thanks for suggestion.

[Stevem]

Check the solder connections on the output tube sockets for rings around them,as this is common in these amps, even more so after pushing tubes in and out a few times.

[pmdez]

Looks like my problem is solved. Seems like one of the tubes (ECC83-S) is damaged. I've replaced it with one of the old 12AX7 and problem disappeared.

Thank you for help

[alternativeleon]

I have the same Issue, I have an Hot Rod Deluxe III, bought an JJ12AT7 and the same Hum at lower volumen and noises, sometime turning off and on the Bright Switch helps, but when I swap back the 12AX7 the problems goes away, I think I'm going to order de 12AY7 or the 5751 from other company than JJ just for checking it out, I'm going to post what happens after this next tube swaps, but Is there anybody kind of knows if maybe the circuit, or some amps have issues with this swaps, or if is just the JJ brand, also going to buy another brand of AT7'S just for the sake of seeing what and what not works!!!

Also I got a Bucear V22, and I swap the first tube for the JJ12AT7 and the amp overdrive channel sounds better, but it did get lot quieter but still gigable, well many thanks friends and hoping to posting soon the results for more tubes