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TAD (Tube Amp Doctor) ToneBone - Pentode

Tube Amp Doctor ToneBone - Pentode

1.75 1.75 out of 5, based on 1 Review

Replacing a pair of EL34 tubes with EL84 tubes by using the TAD ToneBone Pentodes. Solved the problem I had with dissipating too much heat in the powerbrake (waste of energy) but also killed some of my tone.

16th November 2013

Tube Amp Doctor ToneBone - Pentode by Luny Tune

  • Sound Quality 1 out of 5
  • Ease of use 4 out of 5
  • Features 1 out of 5
  • Bang for buck 1 out of 5
  • Overall: 1.75

Here's the original review! See below for my added comments!

I'm reviewing the ToneBone Pentode here as a substitute for keeping in a pair of EL34 and the purpose being that I'd like to waste less energy when diming the amp going into a power brake.

On one hand:
It makes good sense of course that I can dampen the signal appr. 10 dB less with the power brake and get the same resulting volume and the power brake's three power resistors and the three large heat sinks they're mounted on hardly get warm. It's nice to not waste all the heat a 50W or 100W amp would generate and force the resistors and heat sinks to dissipate and get rid of.

On the other hand:
It's a hard rock album I'm recording. The amp is losing it's bite. It sounds good. I'd say quite good...but not as great as it does with the EL34 pair in it. It's too nice now and it's pulling back into the speaker. Additionally, the amp is a little noisier now. Hiss is becoming loud enough for me to start thinking about a gate when recording but even so the hiss is now audible when I'm playing. It's not much, but it's there at , to me, an unacceptable level. If playing with very clean sounds you probably wouldn't notice but I'm REALLY letting my output tubes have it with a signal already driven hard in the preamp. I was speaking to a smart guy I know about it and he suggests that it probably has to do with diodes in the design of the ToneBones themselves, but that's just a theory. Backed, though, by the fact that usually an EL84 isn't particularly noisy.

It's very simple: Tone is king! I'm changing back to the EL34 pair again.

My amp is a Soldano SLO-100 modded to take EL34 instead of 6L6. The EL84 just doesn't measure up in character. In fact I think it's closer to the 6L6 that I'm already moving away from but it also lacks the 6L6 big bottom end.

The ToneBone is easy to use. I did have quite a lot of trouble getting them into the sockets in my amp though. I filed the pins and the guide in the middle a bit, worked, wiggled and worked...and filed...and wiggled some more until I got them seated properly. I'm open for the possibility that the sockets in the Soldano aren't fantastic, so although I've changed tubes in it before without it ever being a hassle like this at all, I'll give them the benefit of the doubt. I also know of others who have had absolutely no trouble pushing them into the sockets. So yes, they're easy to use and the fact that you don't need to re-bias or anything, enabling you to pop them out and pop the regular tubes back in, is a very nice feature. Especially with amps that you need to disassemble to adjust bias on. That's something I'll never learn to understand - why it hasn't been made easily accessible on all modern tube amps? It's downright stupid to have to go through all that just to adjust bias on your amp....well...

I'm not a big fan of some of the classic Fender amps, but I think that the EL84 would actually be a much better choice for me in, say, a Twin Reverb than the original. Those amps have the presence of an icepick in my opinion and the softening up that happens with an EL84 may very well be the cure I would be looking for there. But that's not what I tested here. I just wanted to mention that I do see the potential for that.

Less power means less heat dissipation - Nice!
Easy to use and to change back forth between tubes - Nice!
A little noiser when amp is driven hard - Bummer!
Sounds a little duller that the higher power tubes - Bummer!

This has to land right in the middle. The ToneBones themselves work just fine technically but paired with tubes that kind of defies the purpose, unfortunately it's not a solution for me.

Added comments:
I have of course given these babies a chance to convince me otherwise. Sometimes you notice new things when you've used something for a while. You kinda learn to love it, and so I wanted to let them sit in the amp for a while and record stuff...experiment a little... It wasn't that they sounded bad. They just didn't sound as good... Well, now they don't sound at all.

When turning on the amp a while ago, and after it had warmed up for 20-25 minutes I flicked the standby switch and hit the string a bit to check that sound was coming through. For the first 3 seconds it sounded fine but suddenly lost volume. Significantly lower output. I immediately worried that my power brake was maybe faulty, turned the amp off and checked it thoroughly... Nope, it was all good, so I switched the amp back on.

I kinda recognized the sound character from when bias is waaay too low. When I turned down the volume on the guitar I couldn't get a clean tone even on the clean channel, and I'm sure whatever in the tonebones regulating the bias for the tubes is blown.

I pulled out the Tonebones and put the EL34 tubes back in. Voila! Everything is back to normal.

I have to revise the score. They're still easy to use so I kinda have to stand by the "Ease of use" score, but "Sound quality", "Features" and "Bang for buck" has to receive the lowest score since the damn things break down.

That's just not good enough, TAD! I sincerely hope I'll get my money back.

Last edited by Luny Tune; 9th December 2013 at 01:43 AM.. Reason: One or both tonebones are now defective after only a couple of hours of use!

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