Metropoulos Forum

I've been using a homebrew amp (hot rod cascaded marshall style preamp) with a Soldano SLO power section for the past few months (although it is only 2 x 6L6 instead of 4). It's currently populated with a pair of TAD 6L6GC-STR, with a plate voltage of 504V, a screen voltage of 495V and a bias current of 35mA (+-1mA) per tube. It sounds great at low and mid volumes, but when it's cranked, the bass is a bit too loose and blooms a bit too much. Based on the data below, what tubes would you recommend to replace the chinese TADs and tighten the bass? I asked Watford valves here in the UK and just got a comment stating that 504V was too high for anything except NOS Philips 7581a's. That wasn't exactly a detailed list of suggestions!!!

Currently...

Plate voltage 504V
Screen voltage 495V
OT: 50W, 4K4 primary
Max heater current available: 1.8A per tube
Grid resistors: 5K6
Screen resistors: 1K 5W

Thanks in advance for any suggestions.

My experience with Winged Cs is that they sound great!

Not sure about the plate voltage though.....

In my experience, 6L6GCs tend to have tighter bass than EL34s. It can be overly pronounced, sometimes woofy, though. You could try tweaking the circuit a little, to roll off some bass.

Assuming you have .047 caps to the output tubes and 220k bias splitter resistors, you could reduce those resistors to 100k. This will roll off some bass going to the output tubes and might be a quick, easy solution.

Plenty of people are running higher voltages than yours with various tubes, so I don't really know why Watford would say that. He's probably just going by the data sheets.

If you want to try some different tubes, I would suggest a pair of relatively high emissions RFT EL34s. GE or Sylvania 6CA7s would probably be even better for your application. Yeah, you could try Winged =C= EL34s. They're kinda boring, IMO, though...

Kevin wrote:Assuming you have .047 caps to the output tubes and 220k bias splitter resistors, you could reduce those resistors to 100k.

If I take the amp apart again I think the wife will kill me

Kevin wrote:I would suggest a pair of relatively high emissions RFT EL34s.

Sounds like a plan... I fancy a new flavour of ice-cream.

Check your PMs.

Most USA 6L6GC will withstand close to 500 plate volts, can you drop your screen volts down some?

I agree USA Sylvania 7581 are probably what you want but big bottle Sylvania 6L6GC twin getters are identical in construction and almost exactly the same tone, but the 7581 test out at a little more dissipation (clean headroom).

Derek Trucks uses 7581 in his Super Reverb and he is on the neck PU all night meaning he is pushing a LOT of bass from his Sg into the SR.

You will get more clean headroom from 7581 over what you have now and a bit more bass punch.