Kt90s

[Philv]

Can soneone spread some liht on kt90s please?

Are they a newish valve?

I dont see any NOS versions out thre.

Are there any other valves that are a direct replacement?

Is it worth swapping jinvana kt90s for something NOS.

Cheers

Phil

 

[Earnest]

Are they a newish Valve?

Depends on what you mean by "newish". But no........... KT 90's have been around quite a while.

"Are there any other valves that are a direct replacement"?

Consult your valve amplifier manual... various options should be given, i.e. KT 88 or 6550 etc. If in doubt contact manufacturer / supplier etc.

"Is it worth swapping Jinvana KT 90's for something NOS"?

F**k knows. If you can pick up various KT 90's from other manufacturers at a cheap enough price and your amp is AUTO biasing then why don't you give it a go for the cost of a few pints.

 

[Tel]

I have never heard of Jinvana, are they a manufacturer or are the valves rebadged?

 

[vacdac]

I believe the newish KT120 can be a drop in replacement for KT90/88 too. You wont find any NOS of these obviously, as the nooo kids on the block. User feedback seems fairly positive & providing your amp is compatible they should give around 15/25% more power output IIRC. My understanding is more recent KT90/88 amps are more likely to be compatible & that it seems to be dependent on Traffo specs. :? Valve prices for these seems pretty good for power tubes & providing your amp is compatible they seem worth a look.

 

[Philv]

I have never heard of Jinvana, are they a manufacturer or are the valves rebadged?

I think they are made for or by ming da.

I think i can use kt20s.

of course its not auto biasing - forgot about hat.

They cost around 150 a pair - which seems alot.

Not sure if that reflects the quality or whether it reflects the fact hat ney are ming das own.

 

[Cable Monkey]

The Kt120 is an electrical match for the 6550 and latter day KT88. However it draws a significant amount of extra heater current and so is not to be considered a drop in replacement. I believe KT90's are a higher output version of the 88 but you need to get hold of pre NATO attack EI ones. You will probably get more mileage sourcing quality KT88's.

 

[Petrat]

Hi Phil. I talked with Mark at Ming Da UK about this a couple of weeks ago in relation to the B902. He was suggesting I try the KT120, as it is more rugged than the KT90, and he reckoned it would have a really long life. I got the impression that he'd tried them in the amp. He did say the amp would need re-biasing. I asked about any extra heater current demand and he said it would be OK. However, I later checked some specs online and wasn't convinced, but maybe the Ming Da ones are OK? Anyway, suggest you talk with him

 

[rabski]

Check with the manufacturer of your amp.

KT120 does not, AFAIK draw greater heater current. However it does draw greater HT current.

It stands to reason that if it delivers greater output, then that has to come from somewhere. The rest of the circuit needs to be able to cope. Particularly output transformers.

Check and double check.

Personally, if presented with an amp designed around KT88 then I'd be inclined to look at better KT88s.

 

[Philv]

It doesnt sound straight forward what with the rebiasing, etc

Ill see how it sounds with some nos mullard 12au7 valves first.

Already sounds excellent so that will be interesting next week.

 

[George 47]

Anyone any information on the KT150s which seem to be a grown up version of the KT120s?

 

[rabski]

Biasing is pretty straightforward, and you'd have to do that even with a straight swap.

The simple question is whether the circuit is capable of dealing with the additional current draw of KT120s. Probably it is, as if the HT voltage stays the same, then the KT120s will be under-driven and will behave electrically much as the KT88s would. However, in that case I'd question whether there might not be a bigger gain to be had by using really good KT88s in the first place.

YMMV.

To be honest, the surrounding circuitry means far, far more than the actual tubes.

 

[Cable Monkey]

Modern KT88's and 6550's are spec'd at a heater current draw of 1.6 amps. The KT120 is spec'd at 1.7 to 1.95 amps. It is most likely that transformer winding that will burn out if it is too frugally specified. To give an example a quad of 120's may draw up to 1.4 amps more than modern 6550's.

 

[rabski]

Modern KT88's and 6550's are spec'd at a heater current draw of 1.6 amps. The KT120 is spec'd at 1.7 to 1.95 amps. It is most likely that transformer winding that will burn out if it is too frugally specified. To give an example a quad of 120's may draw up to 1.4 amps more than modern 6550's.

Not so sure Henry.

Genalex and similar quote between 1.6 and 1.75A for KT88 heater current.

That makes around 7A and nobody with a tenth of a brain would spec the heater supply at less than 8A for a quad of KT88/6550.

The Tungsol KT120 spec states approx. 1.7 - 1.95A heater. Any KT88 based amp that can't cope with under 2A heater draw per tube is stupidly under-specced and likely to blow up no matter what it's running.

The real issue is whether there's any benefit, and unless you can provide some more HT volts and current, then I don't think there is. Far better to look for a really good set of NOS KT88 IMHO.

 

[Petrat]

Just to clarify my earlier post ..

The amp in question comes with two KT90 Chinese valves (one per channel, single-ended configuration).

I believe that Mark at Ming-Da UK was recommending the KT120 to me not to get more power from the amp*, but more as a means to further reliability/longevity, the KT120s being more rugged and operating less close to their performance limits than the KT90s (if biased similarly).

* nor indeed to change the 'sound'

Phil .. the various valves discussed above are all from the same 'family', and IMO 'rolling' the power valves won't change the sound of the amp very much, if at all. People usually 'upgrade' through the KT range to get try to get more power, but that means re-biasing and pushing the circuits harder (which is what is being discussed above). Mark was suggesting the opposite, in effect replacing a 100 watt bulb with a 200 watt one, but only asking it to produce 100watts, so less stressed and longer life. Anyway, IME with this amp, your experiments with the small signal 'driver' valve will have far more impact on sound quality.

 

[BD Audio]

I'd get written confirmation from the importer that they will honour your warranty if you proceed.

 

[rabski]

Just to clarify my earlier post ..The amp in question comes with two KT90 Chinese valves (one per channel, single-ended configuration).

I believe that Mark at Ming-Da UK was recommending the KT120 to me not to get more power from the amp*, but more as a means to further reliability/longevity, the KT120s being more rugged and operating less close to their performance limits than the KT90s (if biased similarly).

* nor indeed to change the 'sound'

Phil .. the various valves discussed above are all from the same 'family', and IMO 'rolling' the power valves won't change the sound of the amp very much, if at all. People usually 'upgrade' through the KT range to get try to get more power, but that means re-biasing and pushing the circuits harder (which is what is being discussed above). Mark was suggesting the opposite, in effect replacing a 100 watt bulb with a 200 watt one, but only asking it to produce 100watts, so less stressed and longer life. Anyway, IME with this amp, your experiments with the small signal 'driver' valve will have far more impact on sound quality.

Re-biasing will not change the output. You would need to re-bias when changing any power tubes.

To get the potential extra power output available from changing to KT120s from KT88s, you would need the change the circuitry to increase the available HT voltage and current supply.

Either way, Jack's suggestion is eminently sensible. If you are going to fit tubes that differ from the type originally specified, make sure you get the manufacturer's approval in writing.

 

[Philv]

Thanks all - ill keep power valves as they are for now.

for signal valves i assume changing should not affect the warranty?

 

[BD Audio]

Not if you're using the same type of valve. Mark at MD told me you could run 120 in the B902 but I never tried it and as I say personally I'd want something in writing incase something went wrong...

 

[Mark the Ming]

Check with the manufacturer of your amp.KT120 does not, AFAIK draw greater heater current. However it does draw greater HT current.

It stands to reason that if it delivers greater output, then that has to come from somewhere. The rest of the circuit needs to be able to cope. Particularly output transformers.

Check and double check.

Personally, if presented with an amp designed around KT88 then I'd be inclined to look at better KT88s.

Hi Guys

The B902 does have sufficient capacity to cope with the extra heater current. The bias must be set to the same as the KT90's as this sets the power of the amplifier! Also setting with a higher current will only saturate the OP transformer at high bass peaks, and will over load the rectifier valve!

So setting at 90-95 ma will deliver no more power output, but as mentioned earlier, will give extra length of life for the valves, used at that current in Class A.

The Jinvina brand is the Ming Da brand, specially made for the factory and with so far in my experience a good long life!

Lastly, You can also use KT88 with no problem. But you may need to reduce the bias to limit the current below 90 ma, as the KT90, does just have a little more guts in its design!

Any more info required please do not hesitate to call or email us!

www.mingda.co.uk