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#226 Re: The Newton 300B

Posted: Sat Jul 02, 2022 4:55 pm
by pre65
I'm on BT broadband.

#227 Re: The Newton 300B

Posted: Sat Jul 02, 2022 7:40 pm
by Greg
I’m a Virgin.

#228 Re: The Newton 300B

Posted: Sat Jul 02, 2022 7:42 pm
by Cressy Snr
Ah well it cant be that then.

#229 Re: The Newton 300B

Posted: Sat Jul 02, 2022 11:31 pm
by IslandPink
Greg wrote: Sat Jul 02, 2022 7:40 pmI’m a Virgin.
Get your pointy bodice on and sing about it ! :)

#230 Re: The Newton 300B

Posted: Sat Jul 02, 2022 11:39 pm
by pre65
IslandPink wrote: Sat Jul 02, 2022 11:31 pm
Greg wrote: Sat Jul 02, 2022 7:40 pmI’m a Virgin.
Get your pointy bodice on and sing about it ! :)
Greg in a pointy bodice ? :lol:

#231 Re: The Newton 300B

Posted: Sun Jul 03, 2022 12:29 am
by Thermionic Idler
OK I think Cressy Snr may be on to something actually, this could well be related to ISP. We are with Virgin Media as well - fibre to the property.

Rather depressing as well, if it is ISP specific I haven’t a snowballs chance in hell of resolving it cos as usual in these situations the sods will just blame each other and not lift a finger to do anything about it.

Tonight I’m away from home at my parent’s place in the depths of Wales and suddenly the pictures all load perfectly on my iPad. I think they are with BT, standard ADSL. Greg, Cressy, is your VM connection fibre or ADSL/VDSL?

#232 Re: The Newton 300B

Posted: Sun Jul 03, 2022 7:49 am
by Greg
Mine is fibre.

#233 Re: The Newton 300B

Posted: Sun Jul 03, 2022 9:00 am
by Cressy Snr
We are fibre to the cabinet then coax to the house.

#234 Re: The Newton 300B

Posted: Sun Jul 03, 2022 10:52 am
by Ant
To muddy the waters im on virgin media coax and there are no issues on android

#235 Re: The Newton 300B

Posted: Sun Jul 03, 2022 11:23 am
by Cressy Snr
Safari issue on latest MacOS/iOS/iPadOS maybe?
I went into the quote option for your post and chose the first image, removing the [img] tags so I could send safari after the image directly on the web and below is what came up. Could explain why Android works on VM where Safari will not. There is clearly something blocking secure connections between Apple devices with the latest updates (iPadOS 15.5 build 19F77 being the version my iPad) and your hosting, unless of course your PCs wont cooperate either. Then all bets are off.
158D39C2-EB1B-4A5A-A784-B909B7718CE6.png
158D39C2-EB1B-4A5A-A784-B909B7718CE6.png (150.65 KiB) Viewed 6760 times

#236 Re: The Newton 300B

Posted: Mon Jul 04, 2022 12:09 am
by Thermionic Idler
Steve, that's the exact message I get from Safari. Firefox is a little more talkative:
Secure Connection Failed

An error occurred during a connection to user.fm. PR_END_OF_FILE_ERROR

The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
Please contact the web site owners to inform them of this problem.
It's not a Mac issue, I just tried a wget command from the Linux box running Roon, and got quite a detailed OpenSSL error message which I'll share with Fastmail. I could also see the pictures perfectly, with the SAME iPAD when staying over at my parent's place in Wales last night. Go figure :?

#237 Re: The Newton 300B

Posted: Tue Apr 25, 2023 6:29 pm
by Thermionic Idler
Well, that was a bit sad.

For some time I've been promising myself two pairs of large-bottle ST glass 6V6G's for the driver stage, and took delivery of some matched RCA's over the weekend.

Checked them on my (basic) valve tester to make sure there weren't any shorts, and all looked good, although emission seemed a bit on the low side from one of the pairs - I just put that down to my probably inaccurate tester. Popped them into the amp, listened to a few minutes of quite glorious audio even though it was just an online radio station with the Apple TV - then a 'pop' from the right channel amp accompanied by a white flash from inside the bulb of one of the 6V6's. The stereo image shifts to the left and when I mute the audio, there's a pronounced hum in the right channel, indicating that gain has gone on one phase.

Bugger.

So I now have one matched pair and one orphan 6V6G. Brilliant, when I need four. Needless to say, the Tung-Sols went back in. I don't seem to have a lot of luck when trying to buy decent old-stock valves - shelling out an awful lot of money for stuff that works maybe 70% of the time?

So two things - I need to get that uTracer done once and for all so that I can match the damned things myself instead of relying on hot air from eBay sellers.

Secondly, I'm starting to ponder alternatives to the 6V6 for the 300B driver stage. There seem to be an awful lot of good little tetrode/pentodes about like the EL33, KT61, 6P25 - all of which have the same pinout and about the same 250V / 30mA operating point, and there is sufficient capacity in the heater transformer supplying the 6V6's and 12SN7 for up to 1.1A of heater current, so it's not like I'd have to do any surgery.

The driver stage has adjustable CCS on the anode to linearise them, and they are triode-wired. The power supply limits me to about 35mA idle current.

Thoughts? I know both the Steve's have extensive experience with these as output valves, and that the 6P25 is well liked in particular.

#238 Re: The Newton 300B

Posted: Wed Apr 26, 2023 7:45 am
by ACPEN
Haven't built a PP amp since 1962 - but have you thought of the 6Y6, a very capable driver......

#239 Re: The Newton 300B

Posted: Wed Apr 26, 2023 10:54 pm
by Thermionic Idler
ACPEN wrote: Wed Apr 26, 2023 7:45 am Haven't built a PP amp since 1962 - but have you thought of the 6Y6, a very capable driver......
Haven't got the capacity for the required standing current sadly - I have 90mA to split over two driver valves and the input 12SN7.

Ordered a matched quad of JJ 6V6S today cos I've decided I'm done with being ripped off by the wild west NOS / used old stock valve market, and it's time I gave those JJ's a try. At least if one of them arcs and dies after 4 minutes I can go back to the shop about it instead of having to watch 40 quid go up in smoke cos the fucking eBay seller won't accept returns.

The JJ's seem to be quite well regarded, and if the sound is good I'm just going to stick with them, and only bother with NOS for the input 12SN7, at least you can still get those. Even 6P25's seem to be at silly prices now, I'm on a hiding to nothing because I didn't build up a decent stash when I should have (although I didn't know I was going to need 6V6's until I designed the 300B amps).

#240 Re: The Newton 300B

Posted: Sat Apr 29, 2023 2:53 pm
by Thermionic Idler
Between the anode CCS's on the 6V6 drivers and the 6V6's themselves are 820R Ohmite wirewound resistors. I've just ordered up some Mills 1k resistors to replace them, as that will make the maths a lot easier when adjusting the CCS's. I'm not quite sure what possessed me to pick 820R originally, the value isn't actually that critical so may as well make it an easy one.

Raising it takes a little of the load off the CCS's, but also slightly reduces the headroom - of which there is still plenty, both output and driver stage would have to be badly clipping before the CCS would reach dropout voltage.

I'll be fitting those resistors and giving the amps a general check over next weekend, they have probably had over a thousand hours in service since I last took any measurements. I worked out probably over 4000 hours total, and they are still on the original 300B's, backing off from the original 'hot' operating points has really paid off.

I've been looking back at the original Lynn Olson post on diyaudio that begat this amplifier, and it was posted alongside a related design called Karna Kay, which has transformer coupling for the driver to output stage. At the time I built it I was trying to keep costs from spiralling completely out of hand so I did the cap coupled one, but I've worked out that if I use a Lundahl interstage and migrate some of the circuitry onto PCB's, replacing the tag boards, there might just be room inside each chassis to convert it to the Karna Kay configuration. The B+ on the input/driver power supply will need to come down, my thoughts immediately turned to the Maida regulator that was discussed for a time further back in this thread, there is a heatsink in each chassis that it could be fitted to, and would probably do away with the need for that second 5Hy choke on the drivers.

That'll be a project for the winter if it ever happens, and it'll only be done if I can adapt the existing chassis to do it.

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