KT-88??

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Hey, I have a DSL100HR and was thinking about changing out the EL-34’s for KT-88’s. I heard they sound better with tight low end and more punch than the EL’s. Anyone have any suggestions or input on this? Or has anyone else done this? And what’s your opinion on the sound.
 

Filipe Soares

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Generally speaking the direct replacement for EL34s are KT77s. I have swapped it in my Engl Savage, but being extremely honest it is a very subtle change - at least in that amp.

Only worth it if you are going to retube it anyway.

Speakers will be a way more dramatic change.
 

EADGBE

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Yes don't put KT-88s or 6550s in that amp.
 

Kinkless Tetrode

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The KT88 is the KT version of the 6550. It will most likely require modification to the bias supply circiutry of the amp. The KT88 has a plate dissipation of 42 watts, while the EL34 has a plate dissipation of 25 watts. This will require a different voltage range at pin 5 to bias it properly. Some fixed bias amps have enough range in the bias pot but many don't without specific resistor changes.

As Filipe said, the KT77 is the KT version of the EL34 and will usually go into an EL34 amp with no modifications other than an bias adjustment, which should be done with all tube replacements of adjustable bias amps like the DSL100HR.
 

mickeydg5

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If you can bias a set of KT88 at or below 42mA then you will be fine as is other wide bias will need modification.

Yes 6550 type and KT88 will provide a different feel and lower end. A KT88 may provide a bit warmer and more breakup sound to uppers over the 6550 but the 6550 can be more clear.
 

Pete Farrington

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The KT88 has a plate dissipation of 42 watts, while the EL34 has a plate dissipation of 25 watts
That may be an apples to oranges (absolute max to design centre limit) comparison.
In reality the differential will be somewhat less.
KT88 design max limit is 35W, that of the EL34 is probably about 30W.
 

mickeydg5

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25, 30 or 35 watt plate makes not difference since it should be biased per amplifier design which is that of a 100W. The design made use of 25W power tubes.
 

XTRXTR

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I have EH KT 88s in my 20th Anni 2204. I have not played that in a long time, sounds great. Keep the bias cool, and had to modify the bias resistor, I think...

My shuguang KT 66s are to tall, only fit in my rack mounts 2204 4U height had to set with space for 5U to fit.
 
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If you can bias a set of KT88 at or below 42mA then you will be fine as is other wide bias will need modification.

Yes 6550 type and KT88 will provide a different feel and lower end. A KT88 may provide a bit warmer and more breakup sound to uppers over the 6550 but the 6550 can be more clear.
Yes I’m looking for more breakup
 
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If you can bias a set of KT88 at or below 42mA then you will be fine as is other wide bias will need modification.

Yes 6550 type and KT88 will provide a different feel and lower end. A KT88 may provide a bit warmer and more breakup sound to uppers over the 6550 but the 6550 can be more clear.
That’s what I’m looking for: lower end and a warmer feel
 

neikeel

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I think mickeydg5 was comparing KT88s with 6550s, not EL34s. In general the EL34s will be warmer with more crunch when biased at the warmer end of the safe zone. I really like 6550s for heavy stuff in a JMP100w (biased as 25w tube) and KT88s in a 50w but biased more like 30w but you have to have a suitable PT or you will run the risk of melting it!
To me they are fatter with more body and low end than EL34s. YMMV.
 

Kinkless Tetrode

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Yes I’m looking for more breakup


You will probably get less breakup with KT88s compared with EL34s. If you want more bottom but without later breakup go for the fat bottle 6CA7s.

On edit: And they should go right in with no mods. You must always re-adjust bias on a DSL100, nevertheless.
 
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mickeydg5

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I think mickeydg5 was comparing KT88s with 6550s, not EL34s. In general the EL34s will be warmer with more crunch when biased at the warmer end of the safe zone. I really like 6550s for heavy stuff in a JMP100w (biased as 25w tube) and KT88s in a 50w but biased more like 30w but you have to have a suitable PT or you will run the risk of melting it!
To me they are fatter with more body and low end than EL34s. YMMV.
It seems that is what he is looking for from power tubes. Move away from EL34/KT77 and go to KT88 before 6550 type characteristics.

All tube must be biased according to 25W plate dissipation restrictions for these amplifier designs.
 

neikeel

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It seems that is what he is looking for from power tubes. Move away from EL34/KT77 and go to KT88 before 6550 type characteristics.

All tube must be biased according to 25W plate dissipation restrictions for these amplifier designs.
Yes having worked in DSLs I would be concerned as to how robust the power supply is for anything other than EL34s, although suggestion of fat bottle 6CA7 is a good one.
 

Old Punker

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Hey, I have a DSL100HR and was thinking about changing out the EL-34’s for KT-88’s. I heard they sound better with tight low end and more punch than the EL’s. Anyone have any suggestions or input on this? Or has anyone else done this? And what’s your opinion on the sound.
These EL34's sound like they have more of exactly what you are looking for without changing your tube type. Read the reviews, especially the ones from Marshall owners.


Note: I do not work for, or have any financial ties to the seller. :D
 

mickeydg5

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Yes having worked in DSLs I would be concerned as to how robust the power supply is for anything other than EL34s, although suggestion of fat bottle 6CA7 is a good one.
The design of an amplifier has nothing to do with power supply versus tube type.
The supply only limits what a particular tube can do according to design of the amplifier output section.
If it is 100W then it is thereabout 100W.
 

neikeel

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Oh there is a long delay on the phone line!
I was thinking partly of heater current (but that is 6.4A vs 6A) so not a huge issue, but also the problem with being able to bias them at correct grid voltage not to be too cold to avoid crossover problems and sound bad, never mind the PT being able to provide KT88s with the HT they need to run to provide 200w per quad clean that they have the potential that they do.
If you accept running them ‘at tickover’ then that is fine. In my limited experience of subbing them from EL34 s is that they need to be biased at least as 30w tubes min to sound good. As you know I am not an expert and def an amateur playing with these things.
 

Pete Farrington

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I think KT88 or whatever can only put out their theoretical AB1 max clean 200W/quad given suitable operating conditions. Which are unlikely to be provided by a typical Marshall 100 watter.
I think the bigger concern is people biasing them to idle at 70% of their absolute max limit of 42W, ie nearly 120W idle dissipation for the quad.
Maybe common sense would prevail, but folk are so obsessed with the 70% thing that common sense seems in short supply.
 


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