some schematic questions by newbie help!

Raj1 · 2003-09-08 7:49 pm

Hi,

Regarding this schematic,

http://www.ultranalog.com/cdenhancer/cdenhancer2_3a5.pdf

The 3A5 filaments are on pins 1 and 7,

With + 2.5 volts going to pin 1 and F2 going to pin 7

is this correct?

in the schematic which pin is connected to ground via the 150 ohm
resistor?

Also does anyone have pin data for the AZ1 rectifier???

I'd just like to make sure I'm doing this right, to avoid mishaps, as the voltages are lethal and I'd like to be around to actually hear it work!

Thanks
Raja

fdegrove · 2003-09-08 10:24 pm

Hi,

On the 3A5 the heater is 1 & 7 with pin 4 as the midpoint.

This allows for either series or parallel heating:

2.8VDC @ 0.11A or 1.4VDC @ 0.22A. (According to my RCA datasheet)

in the schematic which pin is connected to ground via the 150 ohm

That would be your cathode resistor, so pin #4 can be used.

Also does anyone have pin data for the AZ1 rectifier???

Yep.
It's going to cost you an O-scope though... :clown:

Cheers,

Raj1 · 2003-09-09 6:37 am

thanks fdegrove

Hi,

Thanks, the O-scopes in the post :nod:

(It was made by the tailor who made the emporer's new clothes :bigeyes:

)

Well I've never used tube re's before and I found it kinda weird that the 4 v ac supply is also connected to the dc output from the rectifier :scratch:

Still I don't supppose I have to understand why???

I have managed to find a cheapo solution for my tmains transfo's,

for the 100v supply and 3A5 2.5 v supply
http://www.maplin.co.uk/products/module.asp?CartID=030909062305883&moduleno=3718&Products=1

and for the rectifier 4v supply

YJ50E on this page
http://www.maplin.co.uk/products/module.asp?CartID=030909062305883&moduleno=3691&Products=11

Can I drop the voltages on all these to the requirements with the use of resistors???

Thanks
Raja

Paul Barker · 2003-09-09 9:45 am

The rectifier chosen is directly heated, this means that the cathode from which we get HT (also known as B+) is heateddirectly by application of 4 volts across both ends.

Therefore the 4v supply to this cathode (known in this case as a filament) stands at the dc potential of the output of the rectifier. Therefore the heater supply must not be used for any other valves and it must not be grounded in any way.

4v is impractical when buying modern transformers, but yes you can use resistors to drop the voltage. Why not instead a 6.3 volt rectifier so you can utilise a 6v secondary? What is the main circuit so we can predict needs of rectifier?

Raj1 · 2003-09-09 5:44 pm

schematic

Hi Paul,

Here's the schematic for the output stage

http://www.ultranalog.com/cdenhancer/cdenhancer2_3a5.pdf

So by your above post even though the 4 v ac supply is connected to the same pin as the B+ output as long as no other circuits are using this winding there will be no problem. I was trying to get my head around how there's no ac leakage into the circuit, but I understand now.

Thanks
Raja

Paul Barker · 2003-09-09 6:10 pm

EZ80 or EZ81 would do B9a socket easy to obtain 6.3v heaters easy to feed.

These are indirectly heated so heater winding is not at HT potential.

fdegrove · 2003-09-09 11:15 pm

Hi,

These are indirectly heated so heater winding is not at HT potential.

No, the IDHT is part and parcel of the final result...

Cheers,

fdegrove · 2003-09-09 11:52 pm

Hi,

My apologies;

The DHT and as such the DHR is part and and parcel of the final result.

Cheers,

Raj1 · 2003-09-11 5:50 pm

3a5 pin 1 and 7

Hi,

Should the 3A5 positive heater supply be connected to pin 1 or 7????

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/3/3A5.pdf

thanks
Raja

fdegrove · 2003-09-11 6:00 pm

Hi,

That doesn't matter, it's left floating.

Cheers,

Raj1 · 2003-09-11 6:27 pm

cheers dude

Cheers mate,

Just ordered the sowter transformers and some tubes...........

By the way from the datasheet I can see that B+ is connected to the white lead???

http://www.sowter.co.uk/specs/8650.htm

Also what are the suggested wattage values for the resistors?

R8, R9 and R10

R11 and R12

R4, R2 and R7 also similar positions for other channel?

I assume that the critical resistors for sound are R4, R2 and R7.......

What's the general preference here for types on the critical resistors, in the UK I haven't seen anyone selling Riken ohm's yet.....

There are bulk foils and metal films, I'm looking for a nice smooth, musical sound....

Have you got that scope yet?

Thanks dude for the service.....

Raja

fdegrove · 2003-09-11 6:43 pm

Hi,

By the way from the datasheet I can see that B+ is connected to the white lead???

Yes, that's it. I prefer the one with the solder tags but that's just me.

R2 +R4 are gridstoppers and are in series with the signalpath, they should be good quality metalfilms, 1/2W would do.

R7 is the cathode R, I'd use a 2W resistor there.

The rest is in the PS I suppose 4W would do.

Check with Maplin or RS components for what they carry in those wattages, better to use a higher wattage resistor than needed since they usually withstand higher voltage better.

If you can find someone selling NOS Holcos then these should provide for smooth sound.

The bulkfoil are fine but expensive. They're often not available in more than 1W ( I think) but you can use them as gridstoppers if you find them.

Dale, Mills,Welwyn are some popular brandnames for resistors nowadays.

Cheers,

Raj1 · 2003-09-17 6:10 pm

pin 4 on socket

Hi Fdegrove,

My 3A5's arrived yesteday, as did the chassis mount sockets for them, however there is no solder tag on the sockets for pin 4, which is left with an empty slot. Given that I'm supposed to connect this to ground, have I recieved the wrong sockets, or is this standard practice? :scratch:

Thnaks
Raja

fdegrove · 2003-09-17 6:50 pm

Hi,

My 3A5's arrived yesteday, as did the chassis mount sockets for them, however there is no solder tag on the sockets for pin 4, which is left with an empty slot.

Uh?

Given that I'm supposed to connect this to ground, have I recieved the wrong sockets, or is this standard practice?

It's definetely NOT standard practice for any socket I know of....

Want you need is a pair of standard 7 pin miniature socket (AKA pico 7).

Cheers,

316a · 2003-09-17 6:56 pm

Re: pin 4 on socket

Raj1 said:
Hi Fdegrove,

My 3A5's arrived yesteday, as did the chassis mount sockets for them, however there is no solder tag on the sockets for pin 4, which is left with an empty slot. Given that I'm supposed to connect this to ground, have I recieved the wrong sockets, or is this standard practice?

Thnaks
Raja

Hi Raj ,
Drop me an email via the system , I may be able to assist with some decent teflon b7g sockets .

316a

Raj1 · 2003-09-17 7:19 pm

Hi,

Just posted an email to the suppliers, lets see what they reply with.............

Thanks
Raja

Raj1 · 2003-09-26 9:37 pm

Hi,

Recieved the bases with the correct number of tags from tube shop, they were okay and understanding about it and sent replacements quickly.....

Using a maplins 100va kit, I've wound a heater supply for the AZ1, using 0.9mm copper wire (supplies around 2 amps), reading at the transformer with no load is 4.1v.

Calculation for the winding was to take number of volts req'd and multiply by a factor of 4.16. This give 16.64 turns, also adding 1% per 10va requirement so around 17 turns.

Hopefully I shouldn't get any voltage sag upon load of the az1, which requires 1.1 amps.

I've also wound another secondry for the regulated supply to the 3a5's, which reads 5.7v at the transformer.....

In any case nearly all the parts are now here, just waiting on the AZ1.........

I have decided to make as much of the circuit on bread board as possible, rather than just go point to point and have wires that are untidy all over the place......

I've made the heater supply and I'm reading 2.87v at the rails after the regulator with no load..........

The B+ supply is almost complete on bread board also.............
.

I plan on having the mains transformers in one corner of the machine, over and around the generic power supply. The AZ1 rectifier will sit in the centre of the top cover of the player, albeit towards the back as the transport occupies the front......

The 3a5's wil be mounted next to each other on the top cover, very close to the output pins of the dac, in order to keep signal wiring as short as possible.

For signal wiring I am using 0.5mm silver wire, and I'm using single strand copper wire - stripped from 30a mains wire to wire the B+ on the bread board.

I'll probably use the silver wiring for B+ connections to the tube pins also.

With reagrds to the choke is this best kept away from the mains transformers and also the output transformers???

In general what circuitry do I need to avoid when mounting transformers and also running mains and signal wiring thru the cd player, that give hum and sound problems???

Thanks
Raja

Brett · 2003-09-27 1:01 am

Re: Re: pin 4 on socket

316a said:
assist with some decent teflon b7g sockets .

316a

Nice sockets. I think I'm gonna get some more next pay.

fdegrove · 2003-09-27 1:09 am

Hi,

Nice sockets. I think I'm gonna get some more next pay.

Need novals too?

I wouldn't mind trading some of my teflon novals for B7Gs....

Cheers,

Brett · 2003-09-27 1:34 am

fdegrove said:
I wouldn't mind trading some of my teflon novals for B7Gs...

The only B7G's I have are from 316a, and his prices are very reasonable IMO, but I'm interested in your novals. Will email.

some schematic questions by newbie help!

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