Are you referring to using NTC thermistors on the DC filament supply?
I regularly use them on the primary side of the filament supply transformer.
I regularly use them on the primary side of the filament supply transformer.
In my experience ntc do nothing for protected units. The initial surge causes an overload in the supply which causes it to "stutter" so to speak. The system works now and startup is very soft and regular. I just hope the sonics have not been ruined. Adding the cap bypass effectively decoupled the gu46 filaments one from the other so that seems a good idea. Small voltage variations due to the ntc's on resistance would also be shunted. Am i missing something?
Thanks as always.
Thanks as always.
Just wanted to inform the folks reading this that the last design works very, very well...
single 12hg7 (cathode biased and bypassed) into gu46. Nice, hum free output!
I will post a video as soon as I can.
for now I have to take measurements and determine the right amount of fb.
given that I am using a 50ohm cathode resistor I figured my fb resistor would be around 2k -5k (must decide after some tests).
cheers
single 12hg7 (cathode biased and bypassed) into gu46. Nice, hum free output!
I will post a video as soon as I can.
for now I have to take measurements and determine the right amount of fb.
given that I am using a 50ohm cathode resistor I figured my fb resistor would be around 2k -5k (must decide after some tests).
cheers
Here is a short video.
10824540_10153618154010400_1003154169_n - Video Dailymotion
Sorry for the crappy quality.
10824540_10153618154010400_1003154169_n - Video Dailymotion
Sorry for the crappy quality.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Right now i am chasing down a groundloop but the amp works as planned.
not exactly... very cheap sockets made for radio use. They come raw and must be drilled to fit the chassis. Not the best solution but good enough. 😉
Again - excellent work ! So how does it all sound in the end ?? What's the rest of your system look like ?
Thank you!
I will be posting videos soon bu the cell phone's mic doesn't do the amplifier much justice.
I can tell this. The amplifier is very controlled and detailed. Woth gnfb the bass is very tight, almost artificial. It is not bloomy or "loud" but very very detailed. Just how i like it (former bass player 😉 )
The mids and highs are excellent. The full "SE" richness is there and the noise floor is very good (not perfect). There must be some ground loops somewhere.
All in all i am very happy. The cheap hammonds are performing very nicely and the tubes are burning in. Transmitting tubes have a considerable burn in time. I noticed this with my gu81m amp. My girlfriend is very happy with this amp and the cat is safe.
I will be posting videos soon bu the cell phone's mic doesn't do the amplifier much justice.
I can tell this. The amplifier is very controlled and detailed. Woth gnfb the bass is very tight, almost artificial. It is not bloomy or "loud" but very very detailed. Just how i like it (former bass player 😉 )
The mids and highs are excellent. The full "SE" richness is there and the noise floor is very good (not perfect). There must be some ground loops somewhere.
All in all i am very happy. The cheap hammonds are performing very nicely and the tubes are burning in. Transmitting tubes have a considerable burn in time. I noticed this with my gu81m amp. My girlfriend is very happy with this amp and the cat is safe.
An externally hosted image should be here but it was not working when we last tested it.
40 euros of material is jot bad for the added safety.
gu46 amplifier - Video Dailymotion
some (crappy) music.
Bear in mind the cell phone cannot record low frequencies..
some (crappy) music.
Bear in mind the cell phone cannot record low frequencies..
Just wanted to provide an update (the last one in order to avoid thread bumping..unless someone has some questions and/or suggestions 🙂 )
The amp works beautifully and really shines now. The gain is not that high but that can be taken care of with a nice tube preamp. Operation is stable and the gu-46 OP point seems to be set. One word for advice is to implement - in all amplifiers based on transmitting tubes - panel meters showing bias current AND an external resistor to modify the current during the amplifier's life. checking tube health is so much easier and practical (can be done by anyone too).
Anyways, GU46 sounds nice. Try it!
The amp works beautifully and really shines now. The gain is not that high but that can be taken care of with a nice tube preamp. Operation is stable and the gu-46 OP point seems to be set. One word for advice is to implement - in all amplifiers based on transmitting tubes - panel meters showing bias current AND an external resistor to modify the current during the amplifier's life. checking tube health is so much easier and practical (can be done by anyone too).
Anyways, GU46 sounds nice. Try it!
Don't know how I missed this thread. Very nice effort! People probably don't realize how big your amp is. I got two gu-46 a while ago, with plans to build an amp at some point in the future. Quick question: did you make your own sockets for them? I can't find sockets for this animal. The only socket on ebay is listed at over $200!
I thought the gu-46 would operate at cherry-red plate but in your pics they seem dark.
I thought the gu-46 would operate at cherry-red plate but in your pics they seem dark.
Well...
1. The plates currently radiate around 150w of heat. Far under the max rating. This however is fine for 30w output. The OPT are the bottleneck and to find larger ones would have place an additional "0" at the end of the BOM. The bias point may not be ideal but works well for my needs. The gu46 operates in SEP mode with 615v on the screen.
2. I found original cheap-o bases made out of a nasty looking flame retardant material. Didn't ask what they were made from, didn't want to know! the bases are real cheap.. basically a round chuck of pressed paper carton 6mm thick with metal pins to accommodate the gu46 electrodes. Nothing fancy, does its job nicely. I installed it so as to allow some movement. this way transportation is far safer and so is replacing the tube.
As far as the size of the amp... I actually pride myself of having been able to stash a lot of gear in a small chassis, but you are right... the requirements are hefty. Each stage is fully decoupled. This alone means that I need to supply at least 3x 1800v capacitor banks. This has equated to around 20v 450v 470uf caps throughout the amp.
The amp does play very nicely. It is very controlled, not mellow and definitely "feels" SS in a good way.... that kind of control over power output that only excellent SS has. for the rest the SEP configuration does result in very tight sound, detailed and refined. Not mellow but then again I don't like mellow amps very much.
1. The plates currently radiate around 150w of heat. Far under the max rating. This however is fine for 30w output. The OPT are the bottleneck and to find larger ones would have place an additional "0" at the end of the BOM. The bias point may not be ideal but works well for my needs. The gu46 operates in SEP mode with 615v on the screen.
2. I found original cheap-o bases made out of a nasty looking flame retardant material. Didn't ask what they were made from, didn't want to know! the bases are real cheap.. basically a round chuck of pressed paper carton 6mm thick with metal pins to accommodate the gu46 electrodes. Nothing fancy, does its job nicely. I installed it so as to allow some movement. this way transportation is far safer and so is replacing the tube.
As far as the size of the amp... I actually pride myself of having been able to stash a lot of gear in a small chassis, but you are right... the requirements are hefty. Each stage is fully decoupled. This alone means that I need to supply at least 3x 1800v capacitor banks. This has equated to around 20v 450v 470uf caps throughout the amp.
The amp does play very nicely. It is very controlled, not mellow and definitely "feels" SS in a good way.... that kind of control over power output that only excellent SS has. for the rest the SEP configuration does result in very tight sound, detailed and refined. Not mellow but then again I don't like mellow amps very much.