Ceriatone JTM45/100 with EL34's question ?

XTRXTR

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Throw 'em in! Unmatched isn't as big a deal as people make out. If you really want, you could match them into two pairs so that the combined current of each pair (ie each side of the output tranny) is similar.

Vacuum tubes are super tolerant. You were just running EL34s at TWICE their design impedance and it sounded great!
Unless you know what you are doing and have the skills to bias your own amp its never a good idea to swap in tubes even when they are the same tube type. There could be many factors at play, its chancy, playing the odds on your amp and putting it at risk. I would not do this myself unless my amp was on my bench and I had the meters and tools at the ready. Tubes are not light bulbs.
 

Kelia

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Throw 'em in! Unmatched isn't as big a deal as people make out. If you really want, you could match them into two pairs so that the combined current of each pair (ie each side of the output tranny) is similar.

Vacuum tubes are super tolerant. You were just running EL34s at TWICE their design impedance and it sounded great!
Ok thanks for the input , was afraid in damaging them !
 

Pete Farrington

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running EL34s at TWICE their design impedance
Could you explain your thinking there?
I wonder if you may be under a misapprehension, eg that valve guitar amps operate using maximum power transfer theorem, with matching source and load impedances.
The output pentodes we use have a very high output impedance, far higher than the load impedance at the OT primary.
The latter is chosen from plotting a loadline on the anode characteristics chart. Phillips provide example typical operating conditions with push pull load impedances varying from 2k8 to 11k. What’s appropriate is determined by the desired power output, operating class, and the anode and screen grid supplies available. With the typical screen grid supply arrangement used in valve guitar amps, the ubiquitous 3k5ish (per pair) OT impedance becomes inappropriate for HTs above around 450V (loaded).
https://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf
 
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neikeel

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Do these graphs help? You can run the numbers yourself here.
The EL34 will give a much greater voltage swing and will certainly sound great until they melt. A quad of KT66 will have less swing and less output but will not melt at these anode and screen voltages.
A quad of EL34s (even the most robust) will only take this for a short while and will need biasing significantly cooler.
 

_Steve

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For the removal of doubt I did not recommend running wrong tubes at a high load impedance. The OP stated the amp he bought came with the tubes that way.

I suggested running his unmatched set of the correct tube type will be fine, and used the example of his amp already running a much much much more out-of-spec setup as a point of reference in contrast to simply putting in unmatched tubes.
 

Kelia

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Question to @neikeel , this Ceriatone 45/100 I have while sounding good, it has
a fair amount of transformer hum and when I look from the top of the chassis ,they seem to be further apart
from each other than the real deal , are yours noisy too ?
Can take a picture if you ask.
 

neikeel

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The early 100w had the OT and PT on axis, changed in 69 when caps went up top.
There is a risk of coupling if the OT and PT are too close.
Some power transformers buzz as soon as they are switched on (in standby by mode). Others hum when switched on because of ground loops, inadequate mains smoothing, poor contacts on switching jacks, ac from heaters etc. You would really need to go through each step logically. The article on amp debugging in Duncan’s amp pages is a good place to start.
 

Kelia

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The early 100w had the OT and PT on axis, changed in 69 when caps went up top.
There is a risk of coupling if the OT and PT are too close.
Some power transformers buzz as soon as they are switched on (in standby by mode). Others hum when switched on because of ground loops, inadequate mains smoothing, poor contacts on switching jacks, ac from heaters etc. You would really need to go through each step logically. The article on amp debugging in Duncan’s amp pages is a good place to start.
Thank you Neil !
 


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