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In the Forum: Audio Discussions
In the Thread: SET amplifiers

Post Subject: It takes time sometimes.Posted by Romy the Cat on: 3/24/2016

Gera, tuning the amp loading is a tricky part. If you deal tube that you do not know and the driver that you do not know then there is no way for you to know the entry point into the game. I think the best way in this situation is not use what people recommend out there or what transformer makers advise to use. Your schematics show 5K into 16R, so use it for now but make sure that it is against 16R. As you set the things up you begin to listen the thing and begin to feel where you need to go, make sure that at this stage your tube is locked in proper operation mode.. The increase load to the tube will give you richer, slower, more harmonic, less detailed and more anti-euphoric sound. To a degree you can test it by shunting the driver by a good resistor of 20-40R. Divide the response of your driver on 2-3 virtual sectors if you horn is between 220 and 2K then observe 220, 1000 and 2000 regions separately as they might be differently impacted by different loading. You might like lower knee with one loading but upper knee with another. If you less load tube then you get "faster" sound, with more transients, details and faster decay. There is no known to me ways to test it beside changing transformer ratio. Transformer taps might be good in here if they made properly (feeling the full bobbin) but I prefer the re-mapable sections. Lundahl makes very friendly transformers for such experiments...

A few warnings. As you change load make sure that you change the tube operation point and keep the tube in symmetric clipping. Idling tube more reduce power and reduce gain of your channel, so make sure that you re-adjust volume on the channel that you are trying to compare. Do not forget that your channel is not alone and it work accompanied with other channels. In some instances, an particularly in your where there is no HJF in band bath, it is preferable to have a channel to be driven a bit too hard (more idle tube) and the shortage of harmonics at lower end to compensate by some overlapping of the next channel at the bottom.

It feels as your channels all have to be load in the same way for own reference impedance but it not might be the case. You need to load each channel in order to get a complete presentation from all channels that you approve. That might take time. Sometime only after a year or two you “get” that one channel might be driven more aggressively…

Rgs, Romy

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