• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

KT88 superthread.

Jump to Latest
#21
Is KR Audio & EAT rebranded Shuguang?

Looking at several tubes we can see that the socket and glass envelope of the Russian (New Sensor) family is very similar and sometimes identical. Same thing can be said about Shuguang tubes with some variation in the socket, but similar. We can also see that the glass envelope has a slightly different shape with a more rounded top than the Russian tubes. (Note that JJ is not New Sensor tube but has similar glass envelope)
​

When it comes to Psvane, the glass envelope looks like the Russian.
When it comes to KR Audio, the glass envelope looks like Shuguang.

Are we looking at collaborations ?
​
 

Attachments

  • Shuguang vs Psvane vs Russian.jpg
    Shuguang vs Psvane vs Russian.jpg
    708.7 KB · Views: 565
Last edited:
#25
Dear All.

I loved creating this thread and I am sure it will help others and perhaps make their life easier in some ways. After much consideration I have made up my mind. If I had to choose a KT88 tube it would be the Shuguang GEKT88 or one its re-branded variants. But I'm not going to. Since the amplifier so far only exist as a schematic, there is room for upgrades and adjustments, therefore, I will settle for the Tung-Sol KT150.
 
#27
KT150 red plating? What diagram or settings do you use? I use some in testing with 600 VDC @100 mA quiescent per tube with UL taps, no red plating ever. Same when driving them to full power, still no red plating. In fact the KT150’s look quite dull. I cannot see if they dissipate 60 Watts (or more), no coloring, no blue glow, absolutely nothing.

I made a mistake only once with a single KT150, shorting the bias voltage and so allowing max. current. It looked like an orange candle and the glass started ticking audibly, even the grids were orange. I was able to shut the tube down before serious damage was done. It’s still good for testing, but not 100% according to specifications any more.

When all my experiments are done with my new setup I will settle with a fresh matched quad.

Regards, Gerrit
 
#28
gerrittube said:
KT150 red plating? What diagram or settings do you use? I use some in testing with 600 VDC @100 mA quiescent per tube with UL taps, no red plating ever. Same when driving them to full power, still no red plating. In fact the KT150’s look quite dull. I cannot see if they dissipate 60 Watts (or more), no coloring, no blue glow, absolutely nothing.

I made a mistake only once with a single KT150, shorting the bias voltage and so allowing max. current. It looked like an orange candle and the glass started ticking audibly, even the grids were orange. I was able to shut the tube down before serious damage was done. It’s still good for testing, but not 100% according to specifications any more.

When all my experiments are done with my new setup I will settle with a fresh matched quad.

Regards, Gerrit
Click to expand...
Thanks for jumping in. Reading some articles between 2013-17 there are reports of the tube red plating even at low bias current. I was looking at some options regarding the KT150 when I ran into these reports. The KT150 require me to alter the transformer choice to accommodate the higher voltage and current need. The goal would have been / is 600-650 plate voltage and 83-92mA which would produce 50-60W, or roughly 70% of max.

The amplifier is designed for 450V plate voltage which many tubs bellow the KT150 can operate at, so the KT150 would require me to redesign the PSU section, select a different mains and OP transformer. Also find a way to adjust the plate voltage between 450V and 650V (max), perhaps through a Pi filter etc. So much more complex. I wouldn't want to lock the amp to KT150 only.

So lots to consider here. The GEKT88 and the KT88-Z/T tubes is highly regarded among many as being stellar tubes. Not knowing about the sonic differences between these and the KT150, I can only imagine.

No matter, my end goal is to have a transparent and open sounding tube with a nice soundstage and instrumental separation and never harsh sounding - to power my tweeter and midrange and allowing a classAB solid state power the woofers.

So what experiment are you performing ?
 
#29
I’m working on a Push Pull amplifier with several stages, not an existing design. I run a 6SN7 Aikido input stage, a MOSFET Concertina, a 6SN7 balanced driver stage, driving MOSFET source followers into the KT150’s. The 6SN7 driver stage and the MOSFET source followers use CCS units 10M90S for current settings. The final stage can be used in UL and Triode mode. Power supplies are all MOSFET regulated, 600 VDC, 400 VDC and -50 VDC, plus an autobias module with it’s own onboard PSU.

The first channel is almost finished, the power supplies have been running for almost a year now (600 V @ max. 800 mA).

My goal is to get at least 50 Watt output with low distortion, 100 Watt will still show some distortion although the numbers are still good compared to many SET amplifiers. So far the sound is good.

Regards, Gerrit
 
#31
This project is still under construction, I edited my schematic diagram today according to my last notes and it’s not ready for publication yet. I do intend to do so later. Perhaps I could give you some partial information in a PM?

I’m using a 440 VAC secundary transformer (toroid). Of course you could regulate the DC voltage further down with MOSFET’s, but doing so you waste a lot of power and generate a lot of heat. KT150’s will do this too as you will know. It would be better to have more secundary voltage switchable, from 300 to above 400 VAC. Or you could put 2 PSU’s in series (450 VDC + 150 VDC).

Regards, Gerrit
 
You must log in or register to reply here.
Top Bottom