Topic: My tube amp projects

[kuton]

I recently posted in Edrel's page two amps using his excellent output transformers. I've also wound a few output transformers and they are no slouches either. One is a 2A3 Single Ended Triode. This is built on a chassis of three aluminium C channels put side by side.



This amp uses 6SL7s in SRPP. The 2A3 is biased hot with voltage of plate to cathode of 290 volts at 60 mA. The tubes are Sovteks which can dissipate a great deal more power. The power supply has UF4007s rectifying the AC. This is followed by a diode damper for the soft start then a choke. In effect, the power supply is a CRCLC. Final capacitor includes a film cap from Edrel. Following is a photo of the underside of the amp.



As I said, I made all of the irons for this amp. The OPT was rewound from a choke I bought in Hong Kong and it shows excellent response to a square wave at both 3 kHZ and 10 kHz. Following is the 3 kHz response.



Then the 10 kHz. There are some wiggles on one of the channels showing that the trannies do not have exactly the same response, but I think close enough. I should try Master Tony's trick of winding his cores side by side to ensure that both cores are wound exactly the same.



This amp is one of my favourites, smooth as only a DHT can sound.

[kuton]

I have found that winding UL trannies are more difficult than for triode amps. I built a Single Ended Ultra Linear amp based upon the Fi Primer 6L6GC schematic. But I used EL34 tubes. Again I used C channels for the chassis.



A view from the bottom shows that I built the amp using tag boards. The coupling capacitor is a vintage paper in oil which gives a smooth sound. All others are common parts. The driver is an EF86 in pentode mode with global negative feedback to its cathode.



I have not been able to get a truly excellent response using UL with global feedback as shown in the 3 kHz square wave below. Still, the square wave looks good with only minimal ringing.



This is the 10 kHz square wave showing ringing.



But the amp still sounds good, and with a power of 8 watts, the amp is good enough for my lower efficiency speakers.

But it seems that famous brands also have a difficulty with SE UL with global feedback. Following is the response of a James 6113 in my 6V6 SE UL amp. This is for 3 kHz.



This ragged response is for 10 kHz. I have not been able to clean up the response using various values of capacitor in the feedback loop.



The James shows much better response in triode mode but will give lesser power. I will install a triode/UL switch on the 6V6 amp so I can get good sound or power when needed.

[tony]

hello kuton, first, welcome to the forum....
it seems your traffo parasitics are responsible for those ringing.....
output traffo's have what is called "funny business", resonances caused
by its shunt capacitance and leakage inductance.....
the object is to get them much higher than 20khz...some had it at 60khz and beyond,
but those would be the most expensive traffos....