Jay wrote:ironman28 wrote:Jay wrote:No Transformer changes? Seems odd since he has been saying not to run anything except 6L6s in these amps. I wonder what made him change his mind all of the sudden? 6550s/KT88s would just require changing a few resistors, and EL34s would require resistors and grounding pin 1 on the power tubes. If they are using stock iron to run EL34s or even KT88s, then you should be able to use KT77s with just a bias resistor change if you want a simple way to get some EL34 type tone.
Well he probably knows the actual ratings of the heater windings on the chinese iron. They might have also upgraded the specs on new production to allow EL34 heater currents. You can test the heater winding by loading it down to simulate the EL34 current to see if the voltage drops more than 10%. The real problem is the rise in core temprature under those conditions.
I added a small 2A filament xformer for $17 to my 50h to run the preamp tubes and use the stock winding for the PA tubes only.
With some 1k sg resistors I can run almost any power tube I want. Also DC elevated the heaters for the preamp tubes.
I'm not confident in the reliability of the stock pwr xformer under stress for long term. It would be nice if JC actually published the design specs.
I like the idea of the filament tranny. $17 isn't bad. How small is it? Shouldn't be too difficult to wire in. I had also contacted Heyboer to make some replacement style Transformers for both PT and OT for the 50H and 100H and had them designed around the SLO spec, but with a higher filament rating. I gave them the dimension of the core and the footprint of the endbells, and they said it could be done, even to make the Hi-Def OT like the SLO has. Prices were VERY reasonable, but I just have not had the time and resources to getting around to doing it.
The tranformer is a Hammond http://www.tubesandmore.com/products/P-T166L6
It is about the same physical size as the choke on the 50H. it is very easy to wire in as the 50h has a jumper that connects the filament traces in the PA to the preamp section. Remove the jumper and wire the new xformer to the preamp. The hardest part was drilling holes in the chassis to pass the leads through. I did have to extend the primary leads to reach the AC input. The only drawback is the amp cant be used with a 220 line input. I will post some pics later.
I like aggressive tone, but not quite as gritty.