Any advice, explanations would be gratefully received.
Its a simple integrated planet horse pc game push-pull amp using ECC83s and EL34s.
They use a 25 volt winding with the heaters in series.
Its best to try match the valves for heater resistance so you get an even voltage drop across each valve.
Not sure if the Jardis have remained the same over the years, but the orchestra's I have worked on did have a trimpot for adjusting the grid voltage.If not, the two blue caps on the circuit board above will be running over voltage.Ive used these figures when re-valving with EL34s with no problems, and the amp sounds fine.Ive been lurking on here for a while now, but this is my first posting.However, Im curious to know how this method of biasing relates to the figures Ive seen for EL34s which suggest that the cathode current should be between 50mA and 30mA, depending on plate voltage.According to the spec it operates in Class A/B and is rated at 40 watts output.Double check that it is a 240 volt version.Edited November 9, 2008 by ehtcom adding to post.
Although I covered basic electronics as part of my maths and physics studies, that was over forty years ago, so please forgive me if I seem a bit clueless!
A inside shot I found on the net below.
Also, as different cathode figures apply to other valve types, how can a single figure apply to the anode measurements, pretty much regardless of valve types?
Im a fairly recent convert to valve/tube amps, and Im trying to get to grips with the characteristics of different valve types and the mysteries of biasing etc.Also, check the heater supply voltage.With KT90s they recommend going up to 120mV.You can just make out the trimpots.My current amp is a Jadis Orchestra.The amp has manual (fixed) bias and according to Jadis can also be used with KT88s, KT90s, 6550s, and 6CA7s.According to Jadis, the same figures apply whether you are using KT88s, 6550s or 6CA7s.Jadis have advised me that the correct bias, using matched tubes, is set by measuring the voltage drop across the.62 resistor between the anode/plate and the output transformer and adjusting the bias pots to achieve a voltage drop of between 90 and 120.Jadis Orchestra Pdf User Manuals.View online or download.