I poste a while ago a few schematics of DC coupled parafeed amp. Here is the latest take, maybe the last one (?). Now a 801A is driving the 304TL. Schematic is pretty simple and straightforward as my way of thinking dictates me
And a pic of the amp: one channel only, +40Kg, 14 irons alas ... too many, electromagnetic pickup can be really a pain. It's laying on the skate I built to move it. I am still waiting for a box to cover and screen the input transformer and the 801A plate choke. That is not the position of minimum hum but at the moment I cannot hear any buzzz in the 115dB horns. Pretty happy about that. The previous version used a 6C45pi as driver that performed better on the o/scope (bandwidth and 10kHz square wave). -3dB points are quite out of the 20-20kHz band.
This is an internal view
LCLC filter and motor run caps in the 304TL psu totalling 200uF. LCLCLC with standard elettrolytics for the 801A driver. CLCLC for the 304TL filaments and LCLC for the 801A. Most of the chokes are two bobbins sharing the same core and in series on the upper and lower leg of the filter.
Sound? Well, right now it is pushing Nick Cave's Dig Lazarus Dig ... you know those beauties (801A and 304TL) are my preferred tubes. GM70 only comes close. I wish I had the famous 75TL to play with.
Ciao
Gianluca
