[Isaacc7]

Well, not being sensible has paid off lol. I have been struggling with the 5b/254m. There was a consistent coarseness through the midrange that I couldn’t shake. Both the Sylvania 14n7 tubes had it as did the b63 Marconi. Tried one of my new Tungsram 12sl7 on a whim. That smoothed things out a bit but seemed to cut out the lower end. Turns out the Raytheon t plate 6f8g is a really good combo with these tubes. It has a pleasing, thick kind of sound. Solid through the mid bass and bass and the midrange coarseness has gone.

I’ve mentioned it before but I think that most tubes can sound good with the right combination. Too often I see people trying a tube and dismissing it as inferior when in fact it is fine. Sure, you could argue that sane people don’t have 15+ input tubes to try with any given output tube but I won’t hear you cause I’ve got my fingers in my ears LALALALALALALALALALALALA.

This is one of the reasons I get FOMO with tubes. What if there is a magic combination just sitting there but I wouldn’t know because “I don’t need more tubes.” Pssh, where’s the fun in that? The problem is that I have found so many great combos and I know there’s more! Still, the wallet is the ultimate arbiter and I must bow down to it. Sigh

 

[mordy]

Seriously 2.0; be sensible with what you are doing. Just buy the right tubes at the right price and then use them.

Bought the GEC A1834 at the right price but I can't get myself to use them...

 

[Zachik]

Bought the GEC A1834 at the right price but I can't get myself to use them...

Easy solution: send them my way. I will use them!

 

[mordy]

https://www.ebay.com/itm/1255565962...6xC0WCsetL%2BQRVNS4DfNFVO6gv3%2F|ampid:PL_CLK
My quad is safely stored away in a safe...

 

[triod750]

I’ve mentioned it before but I think that most tubes can sound good with the right combination. Too often I see people trying a tube and dismissing it as inferior when in fact it is fine. Sure, you could argue that sane people don’t have 15+ input tubes to try with any given output tube but I won’t hear you cause I’ve got my fingers in my ears LALALALALALALALALALALALA.

Agree, it's all about synergy. GE 6BX7GT surprised me by going from pretty boring to pretty good with Cossor 6C5G, tried on a whim. Not good or excellent but much better. Same experience with other combinations. They don't need to be expensive, they only have to be right for each other.

 

[triod750]

Bought the GEC A1834 at the right price but I can't get myself to use them...

Doesn't matter - they are lousy, awful, 'orrible. Waste of money.

 

[Isaacc7]

Agree, it's all about synergy. GE 6BX7GT surprised me by going from pretty boring to pretty good with Cossor 6C5G, tried on a whim. Not good or excellent but much better. Same experience with other combinations. They don't need to be expensive, they only have to be right for each other.

Surprise surprise, I am now using an RCA 6sn7gt clear glass with the 5b/254m and I think this is the best combo yet. I haven't had any success with RCA tubes in this amp in either input or output duties. It's all about the combos.

 

[mordy]

Surprise surprise, I am now using an RCA 6sn7gt clear glass with the 5b/254m and I think this is the best combo yet. I haven't had any success with RCA tubes in this amp in either input or output duties. It's all about the combos.

Yes - it is all about synergy, and there is no way of knowing beforehand, until you try. And this is the reason that I am reluctant to sell any tubes - you never know when that dull sounding and boring tube suddenly excels!
This is one of the aspects of tube rolling that I found very exciting - the discovery that your inexpensive combination sounds just as good or better than the really expensive tubes...

 

[triod750]

Surprise surprise, I am now using an RCA 6sn7gt clear glass with the 5b/254m and I think this is the best combo yet.

The best combo with 5b/254m or....?

 

[Isaacc7]

The best combo with 5b/254m or....?

Yes, sorry, the 5b/254m and the RCA clear 6sn7gt are a good combo. I’m finding it’s more suited for rock as opposed to classical or jazz. The combo is painting with a wide brush but it doesn’t have the ability to slight differences that can bring some instruments to life. For example the Cossor 807 with the 14n7 really allows me to hear the strings and the guitar body resonating distinctly on Julian Bream’s Popular Classics for Spanish Guitar. The RCA/5b254m gives me more of a homogenized sound. Still sounds good but I no longer have the illusion of Bream being in the room with me. An amplified guitar doesn’t have the same subtlety or presence. I’m sure the same will apply to pianos as well.

 

[triod750]

The piano tells a lot about a tube combination!

 

[Isaacc7]

So I had to try it, even if I was tempting fate. Put the kt81 into my amp just to hear what they had to offer. My amp runs in single ended pentode mode with 260v regulated screen supply. According to the data sheet for the kt61 (the octal version of the kt81) I would be just above the optimum screen voltage but below the maximum. I think the anode voltage is just over the maximum. Tubes can run over their maximum but it does age them much more quickly.

Anyway, they sound amazing. Big, warm, detailed, solid bass, the whole shebang. Unsurprisingly they do distort in my amp. It’s just like the 6aq5 which is not surprising since the specs are almost the same. Unlike the 6aq5, the kt81 is pretty rare so I really don’t want to burn these up. Sigh. Would really like to use these. I’ll be able to use the 6aq5 in my new amp but the kt81 (and the 12v version n34) require auto bias. It’s so frustrating owning these great GEC tubes and not being able to use them!

 

[triod750]

Anyway, they sound amazing.

Good!

kt81 (and the 12v version n34) require auto bias. It’s so frustrating owning these great GEC tubes and not being able to use them!

Simple. You just need one more amp. Just one more....

 

[Isaacc7]

Good!


Simple. You just need one more amp. Just one more....

I’m a sick, sick man. My new Ultrasonic Studios amp hasn’t gotten here yet (soon though!) and I have been planning my next amp already. Basically I want a version of what I have right now, a single ended pentode amp. The Dennis Had Inspire KT88 Firebottle is a remarkable amp. Single ended pentode and by changing rectifier tubes you can use output tubes ranging from 6f6 up to kt88. Power output ranges from 3ish watts up to a whopping 10 or so. I want the same amp but designed around lower power tubes like the kt61, 6aq5, etc. that max out around 250v. To help get around the low power I would want it to be a parallel single ended with two or three(!) tubes per side. Of course I would want switchable, or even better variable, heater voltages. And if I’m greedy I would like to switch between ultra linear and pentode. What the hell, why have a cheap output transformer?

The thing is, single ended pentode amplifiers are tricker to design than triode. You need to have regulated screen supplies. And while feedback is optional with triode amps, it is essential with pentode ones. There are many different kinds of feedback; local, global, cathode, Schade, etc. Some of those require careful pairing with the output transformer. Dennis Had (he’s the one that founded Cary amps and is responsible for the popularity of single ended amps in the US IMO) has the formula nailed. Not only do his amps sound amazing, they sound amazing with a variety of tubes. The trouble is I don’t think I can convince him to build to my specs. And even if I could I’m not sure I could afford it lol.

Anyway, yeah, the thought has crossed my mind lol.

 

[triod750]

You are wild and I am crazy....or was it the other way around?