[UntilThen]

Their most common job as voltage regulators were in the computers of the era.

I was on British ICL computers in the late 70s before moving on to IBM. I've not come across the 5998 being used in computers but it probably predates that - like in the 60s. !

 

[Xcalibur255]

Some 5998 are actually labeled IBM for this exact reason.

 

[UntilThen]

I've seen 5998a that are labelled IBM but not 5998 and we do know those are 2 entirely different tubes. Heard both and the 5998a is not fit for my ears consumption.

 

[Xcalibur255]

There are domino plate 5998s with the IBM labeling too. I had forgotten the 5998A even existed.

 

[UntilThen]

In another development, Elon Mask twittered buy 'Signal Advance' and shares in that medical company rose 11,708 per cent in just 3 days. What the investors didn't realise was that Elon was actually saying use 'Signal' in response to using Whatsapp.

Difference in 5998 and 5998a could have disastrous effect lol.

Just kidding but developments these days are astonishing. The world we live in....

 

[leftside]

That's a bit discouraging @UntilThen. I've been hunting for a pair of GEC KT88's for over a year and can't find any in good condition (ideally NOS) that aren't selling for my than my first car. The hunt continues!

KT88 in good condition are harder to find than KT66 in good condition. NOS very rarely come up for sale. The fading/browning getter flashing on the sides give those away as being well used. And if they came up for sale and you purchased them, would you use them? I'd feel guilty. This is why I prefer lightly used tubes. TT21 (with adapters) is an alternative, but those are getting pricey these days as well. Luckily the new production Gold Lion are very good!

The ones that UntilThen showed are from the 1970's, so not as desirable as the ones from the 1950's, but they do indeed look NOS.

Did you know, the very first version KT88 had a brown base and different shaped glass. Good luck finding those

 

[UntilThen]

Leftside has all those that's why I'm going to Canada once restrictions are lifted.

GEC TT21 are still available but please DON'T buy it all. Leave some for me !!!
https://www.ebay.com.au/itm/GEC-TT2...e-also-available-in-pairs-quads-/203075264809

Omg those are in Australia. Hands off everyone.

Ummmm light bulb moment. @Xcalibur255 what do you think of using GEC TT21 in the build? I think it will sound gorgeous.

 

[Xcalibur255]

They seem to be rare and expensive. One of the design goals for the amp was that it not be crazy expensive to tube and re-tube while still sounding great. I also like the power output I'm going to be able to get from the KT150. It's pretty hard to get above 10 watts single-ended without doing crazy voltages and stuff like the 211 or 840 which was a league above where I wanted to go.

 

[LoryWiv]

I currently have Feliks-Audio Elise although follow this thread with interest as I plot my future . Question: Will my 6L6 / KT88 adapters (from @Deyan ) --> allow me to use TT21 in Elise or do I need different adapters, anode cap etc...

 

[maxpudding]

I have an upcoming amp from Mischa as well, I asked Mischa to build me an OTL amp that would run on 6AS7Gs, with the 6J5Gs or 6SN7. Because the BH was originally designed to operate without power tubes, I also asked him if he could incorporate a switch to change the operational mode of the amp (with or without distortion from power tubes). He came back after a few days and told me he could install a bypass circuitry with a switch, and it would be a complicated build. He probably should patent it

Mischa is a great guy, and a talented amp builder, can’t wait to see his creations here in the upcoming months and years.

 

[UntilThen]

What’s that mean with or without distortions on power tubes. What would that do. Just trying to understand from a layman’s perspective.

 

[maxpudding]

What’s that mean with or without distortions on power tubes. What would that do. Just trying to understand from a layman’s perspective.

Basically it means to turn the power tubes on or off that’s all but to do that simple operation would still require a complicated circuitry due to the supercharger in the amp that can’t be turned off.

 

[Xcalibur255]

If the supercharger portion of the circuit acts as a gain stage or has gain of its own then such a switch would allow the amp to operate in a solid state mode if desired. That's the way I interpret it anyway, maybe I'm wrong.

 

[Galapac]

If the supercharger portion of the circuit acts as a gain stage or has gain of its own then such a switch would allow the amp to operate in a solid state mode if desired. That's the way I interpret it anyway, maybe I'm wrong.

That would be very cool, 2 different amps in one. Like a distortion pedal effect on a guitar.

 

[A2029]

If the supercharger portion of the circuit acts as a gain stage or has gain of its own then such a switch would allow the amp to operate in a solid state mode if desired. That's the way I interpret it anyway, maybe I'm wrong.

Not quite, the supercharger essentially works in tandem with the tube by pulling a constant current as a sink. It has no gain of its own and if working properly pulls a constant current no matter what voltage is at the tube anode, such that the tube fully determines the voltage swing that occurs at the anode. The voltage at the tube anode is determined by a constant current source that keeps approx 6.2mA passing through the tube.