so I changed the tubes in my Herbert...

[axeman81]

Yesterday I swapped the complete set of preamp tubes in my Herbie, to Ruby HG+ in V1 and V2 and "regular" high grade in V3-V6.
I think the ones in it were the originals, TAD highgrade in V1 and TAD selected in V2-V6.

I also went from 4xEL34+2x6L6 =c= SED in the power section, to 6xEL34 =c= SED, all pairs biased at 70mA.
The EL34's that were in there before went up to about 95mA after replacing the 6L6 pair with EL34, is this because they were affected by the 6L6 that were removed..?? I thought that that was rather weird. The EL34 tubes that were there before were biased at 65mA when I put them in, so I wouldn't think that they would "fluctuate" over 30mA on their own..!!!

Funny thing was, when biasing the power tubes I cycled through the pairs adjusting each pair at a time, but suddenly when I was about to repeat the whole procedure a second time, I turned the amp on and the mains fuse blew immediately! I thought one of the tubes were bad or something causing the mains fuse to blow, but I couldn't understand what it was..!! So I changed the mains fuse and crossed my fingers...turned the amp back on and everything was fine! I couldn't understand why the mains fuse had blown but I was just happy that everything was OK afterwards

I really like the change in sound now, I see why Peter recommend all EL34's. The amp is so heavy in itself that it doesn't become "mid overkill" even when running all 34's. However I didn't like the amp so much with the stock TAD EL34's in it.
Also, Channel 3 has a lot more gain than before, I -think- this is because the stock preamp tubes (TAD) was not a high grade in V2 but only "selected" grade so I assume it had less gain than the new ruby HG+ in V2.

When rolling off the gain on Ch3 it's really heavy for riffing, I never used it for anything else than solo's before so that was a nice surprise
Also, maybe it is a placebo effect, but I -think- both channels 2 and channel 3 now has a bit lower noise floor, it was very very quiet
I think the biggest change is because of the new preamp tubes, not so much the removal of the pair of 6L6.

I only had time for a quick test to check that everything was alright no microphonics etc., but I will report back after the gig tonight how it sounds on full blast at the venue
Thank you again Peter, for building this great amp!


best regards,

- Rune

 

[MARK2C]

Each tube has it's own current draw, so when you adjust one you need to adjust them all again until they balance.
Biasing your Herbert one pair at a time does not mean they are all adjusted perfectly when you are done. You have to go over
them each three or four times until all three duets meet your desired bias setting. I used three screwdrivers to make this quicker,
but in the end each duet is matched at 70mA. If you put a different tube type duet in and it has a hotter or colder draw it makes the other
sockets bias go up or down so being patient and adjusting slowly is the best way to ensure you don't get a pair that spikes and blows the fuse.

 

[HumdinGer]

Also, maybe it is a placebo effect, but I -think- both channels 2 and channel 3 now has a bit lower noise floor, it was very very quiet
- Rune

One should never disregard the feeling that's often referred to as placebo. My experience is that very small changes in the sound, often referred to as placebo from doubters, can be THE very thing that differs extremely good from absolutely amazing! Like on my hi-fi system... Two components that apparently sound exactly the same, but still... One of the components makes me bored after a while, but the other just makes me put on record after record. Placebo? I think not

 

[King Crimson]

The EL34's that were in there before went up to about 95mA after replacing the 6L6 pair with EL34, is this because they were affected by the 6L6 that were removed..?? I thought that that was rather weird.

Not unusual at all when mixing different power tubes. That's why as a rule of thumb you must always re-bias, even if you are replacing the same type of power tube.

When rolling off the gain on Ch3 it's really heavy for riffing, I never used it for anything else than solo's before so that was a nice surprise

Hello, that's what CH2 is all about. CH2 is the most versitile channel on Herbert.