I assembled a Elekit TU 8200 and use stock 6L6GC EH. Photo here https://www.flickr.com/photos/64618899@N04/25460936590/in/dateposted-public/
6 months into use caught tube rolling fever. The amp is auto biasing. Got KT88, 6CA7 and EL34B. Tried out KT88 - a big change for me from stock tubes.
Would using two different tubes in the R & L channels damage my amp? Wanted to compare how each tube sounds against the other. Perhaps a redundant question as the two channels are independent, still they share the same PCB, power supply, heater supply etc.
Thanks
Subramoniam
6 months into use caught tube rolling fever. The amp is auto biasing. Got KT88, 6CA7 and EL34B. Tried out KT88 - a big change for me from stock tubes.
Would using two different tubes in the R & L channels damage my amp? Wanted to compare how each tube sounds against the other. Perhaps a redundant question as the two channels are independent, still they share the same PCB, power supply, heater supply etc.
Thanks
Subramoniam
Hmm....
Daft thing to do!! Lets just bung this (Totally Different) valve in this hole in this cheap Chinese amp!
(Maybe I'll burn the house down tonight too.....)
Cheapo Chinese Valve Amps and Safety Margins are Usually Mutually Exclusive Expressions, I should know, Ive Got One! (Completely Redesigned I must add)
I Really Hope you have thrown away the original Power Cable it came with--Death Trap in Cable Form!
Consider the 6L6 tube has a 0.9A heater at 6.3V--The Correct Original Valve for this amp you say.....
Consider the KT88 tube has a 1.6A heater at 6.3V
Consider the EL34 tube has a 1.6A heater at 6.3V....
--Just in this small fundamental thing--Not considering all the other--Much Bigger Differences between different valve types--Just because the thing will fit--and sorta work--doesn't mean its OK!
Auto-Bias--Isnt Automatic between Different TYPES OF VALVES! Its Preset During Design, involving a Resistor Value. Change Valve Type, Resistor will need changing to give Correct Operating Point for Replacement Valve.....
Examination of its Schematic shows no special arrangements for automatically detecting and altering its bias due to tube substitutions, its just a plain common or garden resistor from cathode to deck--1930's style auto-bias.
Running KT88 will seriously Overload the Heater Supply of the original design intended for 6L6 valves, by a factor of Over 50%! Let alone any excess Current drawn due to the Wrong Bias Resistors and different valves....
--Using these for any length of time--Its a wonder it hasn't fried the Mains Transformer already!!
Daft thing to do!! Lets just bung this (Totally Different) valve in this hole in this cheap Chinese amp!
(Maybe I'll burn the house down tonight too.....)
Cheapo Chinese Valve Amps and Safety Margins are Usually Mutually Exclusive Expressions, I should know, Ive Got One! (Completely Redesigned I must add)
I Really Hope you have thrown away the original Power Cable it came with--Death Trap in Cable Form!
Consider the 6L6 tube has a 0.9A heater at 6.3V--The Correct Original Valve for this amp you say.....
Consider the KT88 tube has a 1.6A heater at 6.3V
Consider the EL34 tube has a 1.6A heater at 6.3V....
--Just in this small fundamental thing--Not considering all the other--Much Bigger Differences between different valve types--Just because the thing will fit--and sorta work--doesn't mean its OK!
Auto-Bias--Isnt Automatic between Different TYPES OF VALVES! Its Preset During Design, involving a Resistor Value. Change Valve Type, Resistor will need changing to give Correct Operating Point for Replacement Valve.....
Examination of its Schematic shows no special arrangements for automatically detecting and altering its bias due to tube substitutions, its just a plain common or garden resistor from cathode to deck--1930's style auto-bias.
Running KT88 will seriously Overload the Heater Supply of the original design intended for 6L6 valves, by a factor of Over 50%! Let alone any excess Current drawn due to the Wrong Bias Resistors and different valves....
--Using these for any length of time--Its a wonder it hasn't fried the Mains Transformer already!!
The new styling notiwithstanding, the Elekits are actually pretty nice amps. They're from Japan, they are not cheap Chinese junk.
I have a TU-879S and a couple of the other older models waiting to be built.
Win W5JAG
I have a TU-879S and a couple of the other older models waiting to be built.
Win W5JAG
It isn't the cheap Chinese amp. Please check before you write something. As simple as typing "Elekit Tu-8200" in your Google. you can get the manual from Tube Depot website to check the circuit if they have garden resistors blah, blah...
Tube rolling with KT88, KT90, 6550, EL34B etc. have been recommended by Elekit.
Anyway thanks for the loooong advise. I had checked all these issues before trying out the new tubes.
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Elekit kits are pretty well designed and professionally finished. No one would say it was assembled at home. I made TU-8500 as well to compliment TU-8200. 🙂🙂🙂
I'd have fallen into "Chinese fishing net" (it's a real fishing net we have in some parts of South India) had I not read about TU8200 in 6moons, kenrockwell, head-fi etc. plus Victor Kung's in this forum.
Elekit made me revive my DIY Audio. My old Yamaha sleeps now.
It's true that different output tubes will draw differing amounts of filament current,
so watch out for possible overheating in the power transformer.
If the filament voltage doesn't drop much from the 6L6 level, it should be ok.
From the mfr:
"The TU-8200 ships with Electro Harmonix 6L6GC power tubes, but also supports a wide range
of other power tubes such as KT66, KT88, EL34, 6550 (and others) with no modifications and
no need to re-bias."
So, certainly the power transformer is claimed to be adequate for 1.6A filament tubes.
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Elekit are not against tube rolling and that too without any adjustment. I got confirmation email from 'em and Victor Kung before I got my tubes.
Prior to zeroing in on what kit to purchase I had read manuals of available ones Velleman, Elekit and another one I don't remember the name. Only Elekit had this advantage of not having to take off the cover and fiddle with bias and worry about heater current.
well, I guess I can throw out all those pesky data sheets and just rely on the one from now on... Never could get to grips with graphical analysis anyway.
;-)
;-)
Remember that this is a single ended amp, so there's only two each 12AU7 and 6L6
in the entire stereo chassis. That's under 4A total at 6.3VAC, regardless.
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alternatively, with the 1.2A finals, you are within 10% of the maximum rated output...
If the filament winding is rated for 4A, each output tube can draw at most (4A/2-.3A) = 1.7A.
With 1.2A filaments, the current draw is 2 x (1.2+.3) = 3A, or only 75% of the transformer rating.
Transformers can be over driven to some extent. Normally these are not designed to maximum flux density of the core material that they saturate and winding wire cross-section sizes are not so tiny to fuse with a little overload.
Got confirmation from Elekit as well though the manual says KT88 could be safely used.
True - 90% of heater winding not the whole trafo.
Normal trafo burn outs are at primary side due to smaller cross section of the wire used for primary. Mostly if core if undersized it saturates drawing very high magnetising current and burn.
As per the manual the trafo is rated for at least 85W to suit working with KT88. So I have to conclude the trafo is not an issue.
The discussion is now going off topic 🙂.
Got an answer from Elekit there is no problem running two types of power tubes one in each channel. I was wondering if there would be some mutual effect between the tubes due to sharing the PCB, HV supply etc. and did not want to fry my amp.
Mutual inductance, mutual capacitance and coupling, induction, partial discharge, insulation breakdowns etc. are part my work life at several kVs (test voltages of >460kV) so being extra careful.
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