It appears that the 6F1 heater isn't grounded - perhaps that is just corner cutting as the Rhk of each 6F1 would effectively 'ground' the heater winding.
Filament winding for 6F2 preamp/ phase splitter tubes has center tap that is shown in previous posted schematic tied to chassis ground.
I missed this connection at first and experienced low level speaker 'hum'- Correcting this eliminated it.
Jim
I missed this connection at first and experienced low level speaker 'hum'- Correcting this eliminated it.
Jim
Hi!
I bought this kit in late 2021 and got a pcb that has some modifications, compared with the pcb exemplified higher up in the thread. The Rin/Lin via hole is connected to a 0.1uF capacitor. The node that matches the input node on the schematics is marked with a red arrow on the attached jpg.
I've reached out to the vendor, on ebay asking for more info. Has anyone seen this board (attached)?
I bought this kit in late 2021 and got a pcb that has some modifications, compared with the pcb exemplified higher up in the thread. The Rin/Lin via hole is connected to a 0.1uF capacitor. The node that matches the input node on the schematics is marked with a red arrow on the attached jpg.
I've reached out to the vendor, on ebay asking for more info. Has anyone seen this board (attached)?
Attachments
I started to trace the pcb and it seems the 0.1uF is placed properly. However, there is a 0.1uF coupling capacitor that is not shown in the schematics they send me.
Now I've built the amp and tested it. It plays okay but it might be a tad high in the treble range. I might address this by tinkering with the highcut shelf filter sitting between the two stages of the 6F2 tube. 🤔
Some one the parts must be replaced, e.g. the RCA jacks are kind of crap. But overall I'm satisfied with what I got at this price range.
Some one the parts must be replaced, e.g. the RCA jacks are kind of crap. But overall I'm satisfied with what I got at this price range.
Of the amp? In theory it's pretty flat, the shelf filter I mentioned is edging of a tad above 10kHz or so.
Embarrassing...When I did the first start up I plugged my telephone as source. Turns out the phone had an eq settings where some bands in the treble range were raised 1 or 2 dB. 😳
Now the transparency of the amp seems more apparent. The speakers i use, klipsch m160, are a tad base heavy, but its okay. I guess I leave the amp as it is, for now.
Now the transparency of the amp seems more apparent. The speakers i use, klipsch m160, are a tad base heavy, but its okay. I guess I leave the amp as it is, for now.
I completed one of these kits the other day. It sounds quite good into some Fostex full range single driver FF105WKs.
The capacitor quality leaves a lot to be desired (other than the WIMAs). Used decent Nichicons instead of the "musicalnote" caps.
The tube sockets are fine quality, in my opinion. A lot of makers cheap out on those.
The power transformer runs hot as a firecracker after a half hour of use. My mains voltage is 122vac. The transformer states "110v" but, who knows what it actually is. Cannot really go by the ratings on these Chinese parts. So, I have been running the unit off of a 1000VA Variac-style transformer set to 110vac. It runs cooler and sounds the same.
The capacitor quality leaves a lot to be desired (other than the WIMAs). Used decent Nichicons instead of the "musicalnote" caps.
The tube sockets are fine quality, in my opinion. A lot of makers cheap out on those.
The power transformer runs hot as a firecracker after a half hour of use. My mains voltage is 122vac. The transformer states "110v" but, who knows what it actually is. Cannot really go by the ratings on these Chinese parts. So, I have been running the unit off of a 1000VA Variac-style transformer set to 110vac. It runs cooler and sounds the same.
"The capacitor quality leaves a lot to be desired (other than the WIMAs). Used decent Nichicons instead of the "musicalnote" caps.
The tube sockets are fine quality, in my opinion. A lot of makers cheap out on those."
Built same amp April '20 during shutdown- something to do...
My kit had WIMA's for audio coupling- 22uf/400v for preamp B+ filtering. What value are the 'musicalnote' caps?
Jim
The tube sockets are fine quality, in my opinion. A lot of makers cheap out on those."
Built same amp April '20 during shutdown- something to do...
My kit had WIMA's for audio coupling- 22uf/400v for preamp B+ filtering. What value are the 'musicalnote' caps?
Jim
Yes, the WIMAs seem fine in my amp. The musicalnotes are the power supply caps. 330u at 450v. I opted for better quality parts to increase reliability.
Agree,
Supplied RCA's are crummy. Did you notice the stepped insulators required 'massaging' to tighten up on the chassis holes?
Jim
Supplied RCA's are crummy. Did you notice the stepped insulators required 'massaging' to tighten up on the chassis holes?
Jim
Yes, the RCA inputs were a problem for me as well. I was able to use them eventually though. They would not tighten initially.
I'm listening to the unit right now, fed off of a Musical Fidelity VDAC mkII.
The supplied output transformers have plenty of bass punch. I am very impressed with the quality of the Chinese tubes so far. Not microphonic at all, and a great sound.
I have read about rolling in some Russian 6P1P-EV which were made by Svetlana years ago.
If anything, I will begin by trying some GE- JAN 6U8A in the splitter/pre position since I am enjoying the stock finals for now.
I'm listening to the unit right now, fed off of a Musical Fidelity VDAC mkII.
The supplied output transformers have plenty of bass punch. I am very impressed with the quality of the Chinese tubes so far. Not microphonic at all, and a great sound.
I have read about rolling in some Russian 6P1P-EV which were made by Svetlana years ago.
If anything, I will begin by trying some GE- JAN 6U8A in the splitter/pre position since I am enjoying the stock finals for now.
Rolled tubes on original design- tried 6P1EV outputs- no difference my ears could hear. Rolled the preamp tubes... 6EA8, 6U8A, 6GH8
Struggled to find preamp tube better than Chinese tube that didn't have 'hiss' at no volume. Jan 6U8A's started out quiet, then 1 got 'hissy' after 2 months daily use. Bottom line- my rolling showed ChiFi tubes hard to beat in original design.
Then began researching and changed up design w/ diff PCB's (pics)
Blue board- Audio Note EL84 (6U8A/6BQ5) design
Green board- Dynaco ST-35 (12DW7/6BQ5) design
Dynaco design used hi-gain triode as preamp instead of pentode- noticed significant reduction in background 'hiss' instantly.... the floor was almost dead silent... decided Dynaco front end design was a keeper.
Red board is current design- a hybrid really... Dynaco's dual triode front end feeding Pioneer's SA-810 higher power 7868 (6GM5) outputs.
Currently at the point of 'tweaking' values to optimize this design... first upgrading original power transformer to feed higher power output tubes.
Jim
ps. it's a journey; have fun with it... but always be aware that these voltages can be lethal if you dive in ;<)
Struggled to find preamp tube better than Chinese tube that didn't have 'hiss' at no volume. Jan 6U8A's started out quiet, then 1 got 'hissy' after 2 months daily use. Bottom line- my rolling showed ChiFi tubes hard to beat in original design.
Then began researching and changed up design w/ diff PCB's (pics)
Blue board- Audio Note EL84 (6U8A/6BQ5) design
Green board- Dynaco ST-35 (12DW7/6BQ5) design
Dynaco design used hi-gain triode as preamp instead of pentode- noticed significant reduction in background 'hiss' instantly.... the floor was almost dead silent... decided Dynaco front end design was a keeper.
Red board is current design- a hybrid really... Dynaco's dual triode front end feeding Pioneer's SA-810 higher power 7868 (6GM5) outputs.
Currently at the point of 'tweaking' values to optimize this design... first upgrading original power transformer to feed higher power output tubes.
Jim
ps. it's a journey; have fun with it... but always be aware that these voltages can be lethal if you dive in ;<)
Attachments
Interesting findings!
Would you mind posting the schematics for the tweaked version with the 7868 output tubes?
Late getting back- sorry
Final design is still being tweaked. Added some SS on the front end- DAC, phono preamp, Bluetooth, and 7 band EQ. Also in process of upgrading power supply needed for higher power output stage. When complete, I'll post it up- gonna cut new chassis to enclose everything too- SS stuff currently in separate attached enclosure.
Jim
BTW- seems the 6gh8a was the best sub for the 6F2, IIRC
Occasionally I get popping sounds in my amplifier when I have a loud source. Has anyone else experienced this?
I suspect that it is the input capacitor that overloads in some way.
I suspect that it is the input capacitor that overloads in some way.