Curious_George

I’ve never designed or built a parafeed, but they do have great potential from the lack of DC gap. The audiophool guys will cringe at the thought of a coupling cap though! I have a pair of 833A tubes that I bought a long time ago. I was going to bias them at 0VDC, but never got around to building the amp. Even bought 872’s to go with them.

Interesting: https://www.diyaudio.com/forums/tubes-valves/261152-hell-class-a3.html

I typically use 220k. I cut and pasted some of the circuitry from other amps. Thanks for the catch.

I guess "easily built" depends on the skills you have. I frequently forget we are all blessed or not blessed with certain skills. Somethings never change...

They should. The Cornwall enclosure is roughly 15.5 deep. Working depth will be less, maybe 14". The 18 x 10 horn is approximately 7 3/4" deep.

I always tweak the output tube cathode bypass cap in circuit because too large of a cap can give your a "boost" in the low-end depending on output transformer parasitics, etc and then the frequency does not roll-off smoothly. I have also seen the driver tube bypass cap affect the final frequency response with a peak as well. I have an AP, so it is just the push of a button to measure frequency response out to 200kHz in about 10 seconds.

.

.

I chose a chassis bigger than I needed in case Rich wants to upgrade the output transformers in the future. The circuit will be a standard textbook circuit (tried and true), but some tube rolling will be possible mainly for the rectifier and output tubes. The 6SL7GT does not have an equivalent (except a Loktal), so only different manufacturers of that tube will be possible.

I can post a schematic later today. I've got two pair of Chinese 300B's. One pair (Guiguang NGG) came with a 300B Music Angel amp I bought years ago and the other pair is Shuguang. Nothing special, but they have been troopers for all my testing and design work. I always liked JC's version (Micro 3.5) of the Loftin-White 2A3. Never built it, but may one day.

I have used the SRPP as a driver for 2A3 and 300B in addition to the standard common cathode topology. I may use a 6AQ7GT in lieu of a 6SL7, which is 1/2 of a 6SL7 (plus a dual diode), so no paralleling needed there. This is just going to be an amp (versus integrated), so no extra gain by cascading stages will be implemented. I agree that AC would be the most likely to cause filament failure over CC or VS. I’ll be using a 317 for regulating duties and it can be configured for “slow turn-on”.

I’ve used CC, VS and good ole AC on filaments and I can’t say which makes a tube last the longest. Sonically, CC are supposed to be all the rage, but I can’t tell any difference in sound between CC and VS either. Yes, Class A1, 6SL7GT & 300B.

Power switch (no matter the position) does not imply anything.

.

.

Roll your own with Zig-Zag, to take off the rough edges (zig zags).

Great pictures. It's nice to see children who actually want something that their parents had and are willing to "pass it down".

Those conditioners should have circuitry similar to the Tripplite.

If you don’t find any for sale, there is enough documentation floating around for an ALK Universal clone to be easily built.

In the end that is what it is all about - fun & enjoyment. Having multiple crossovers for a speaker is like having multiple amps or speakers or anything else audio related.

On 11/16/2021 at 8:59 AM, joeward said: "I wonder if someone with more tube experience than I have can answer a question for me. Does it take a few minutes for a Conrad Johnson PV2 to stabilize after flipping it on? Seems I can get some nasty feedback from it through my speakers if I turn it on immediately but if I warm it up for a few minutes before turning on my amp it's dead quiet in that regard. Sounds really good too. Just concerned their could be a problem that needs checking out. Thanks!" "That is certainly a sign of instability with the amplifier. I highly recommend getting it to an amp doctor right away before you start burning up speaker parts from oscillations. You may only hear the noise during power up/down but it may also be present during listening but above the range of hearing, most oscillations I find in tube amps are between 30kHz-60kHz. Sometimes you may notice the amp sounding a little fatiguing to the ear or most likely you don't notice anything until speaker parts start to fry or eventually the issue gets so bad the amp gets further damaged. Squealing during power on/off is in no way normal." From your description, it could be "normal"operation. When I have used tube preamps in the past to drive solid-state amps, if your turn-on sequence is not correct, it is possible to get thumbs, buzzes and noise from your system. The noise you heard may not be "feedback", but just a noise. For example, if you turn-on the amp first, then the tube preamp, you may hear something in the speaker as the preamp slowy turns on (such as the voltage across the output capacitor charging up). This could induce a slow DC-Offset into the signal chain. I have heard this before. Always turn-on the preamp first, then the amp and the opposite when you power down - amp 1st, then preamp 2nd.

Did this issue just arise or has it always done this? Give us some history of the unit.

Understood. Perhaps look elsewhere in the audio chain to spend money on the "upgrade". Unless you have money to burn. I'm not hurting for money, but I always look for a good value. It's just me. In addition, because I have so many hobbies, it helps spread the money around!

If a vacuum tubes need anything done to it before you use it (except if you want to match them for various reasons), be wary.

I’ve used these in the past as an example. The new PSvane 845’s appear to be well made and are about $150 a pair.