417A Line Amp

[fdegrove]

CATHODE BYPASS.

Hi,

Since I have more gain than I need in the system, I'm also tempted to unbypass the cathode resistor. Anyone try this?

Since you use a WOT, I would gladly do away with any cathose bypass cap here...

After all it slows down transient response and in this case you hardly have to worry about Zo.

Cheers,

/less is more mood tonight...

 

[apassgear]

Re: OSCILLATIONS AND GRIDSTOPPERS.

Hi,

Of all the Stabivolt tubes the 90C1 is one of my favourites together with the 5651A.

Re: gridstoppers, if you don't need them, don't use them.
Contrary to what you may read they kill detail and dynamic range suffers too.

Cheers,

Frank,

Checked on those glowers and they seem to work to a lower voltage that what I would like, something like 90V and the 5651 will allow up to 3.5 mA?

What I'm looking for is something on the 110-120V range with aprox 20 mA to use WOT.

Regarding those gridstoppers I agree 100% with you based on the test I did during the weekend. I was previously well aware of your opinion about these R's and that was the reason I did the test!!!

 

[fdegrove]

GLOW DISCHARGE.

Hi Tony,

Checked on those glowers and they seem to work to a lower voltage that what I would like, something like 90V and the 5651 will allow up to 3.5 mA?

Yes indeed, I was speaking generally.

The OA2 is a 105V zener, I use those too but strangely enough they tend to sound...dare I say it...rather cold in comparison.

Odd,isn't it? It maybe due to the different gas, I really don't know.

I was previously well aware of your opinion about these R's and that was the reason I did the test!!!

Thank you. I feel honoured by all the trouble you went through.

Cheers,

 

[apassgear]

Re: GLOW DISCHARGE.

Thank you. I feel honoured by all the trouble you went through.

Cheers,

No trouble at all, that's the spirit of DIY's. In any case I will insist on not using the GS, will try the ferrite beads as suggested by Gary.

 

[fdegrove]

FERRITE BEADS.

Hi,

will try the ferrite beads as suggested by Gary.

They work.
Just make sure they're fixed into place on the wire, I simply glue them on the wire so they can't short anything out.

As with the GS they are most effective when closest to where they should be: a grid or even an anode.

Happy listening,

 

[apassgear]

Re: FERRITE BEADS.

They work.

Order in house once again.

Changed the GS with a piece of wire and a ferrite bead close to the socket tag, added a small drop of epoxy to fix them and ready.

Connected to the system and from the start things changed and it was obvious that the previous unbalanced sound was over.

Though it took about 3 + hours for breaking-in and still not done completely (break-in for a 4 Cm wire and two solder joints ??? )

IM and THD seems to have been squashed. A much transparet and deeper soundstage plus lots of more details.

Thanks to all for the input

 

[siu sin man tho]

hi, really good handcraft.
Do u use trans couple pre-amp out .
I also use 417a pre-amp.
output I use 10K or 20K :600ohm output. really very good.

thanks

Thomas

 

[apassgear]

Hi Thomas,

Thanks for the input and prise.

I still don't have an OT.

I did order some M-6 (EI-100) lamination to roll my own OT with a 5K / 600 Ohms impedance but after calculating the minimum number of turns needed for the primary (6000, using a 38 mm stack) I got quite lazy to start the job.

Which transformers are you using?

10 or 20 K seems a little to high?

I have been very pleased so far running the stage with a 5K resistance loaded plate even though they are cheap carbon films with magnetic caps!!!

What boders me most on the actual setup is the high gain of the stage for which I have to keep the grid very close to ground in order to control the gain with the attenuators. But that does not seem to degrade the sound, but have no way of comparing.

 

[siu sin man tho]

I test many types. at last i made two choice. use 6sn7 use the photo shows.
if use 417a use tango NP-216.

the middle one is pre-amp.

thanks

Thomas

 

[apassgear]

Zen aproach???

Woooooow Thomas.... a gift to the eyes!!! You got there some very very nice gear!!! Congratulations for your excellent work

If you have not done so yet you should post a new thread for each of those creations!!!

I see some Bartolucci tranies on your preamp?

How much those Tango's NP 216 cost in Hong Kong???

 

[siu sin man tho]

Hi tony,

5 K also Ok.

the pri winding resister at least 3 times more than the plate load.
if more will less the THd will lower. but less output. mainly is the bandwidth & the henry of the primary winding.

Hope can help & glad to talk to U.

thanks

Thomas

 

[siu sin man tho]

hi,

is your circuit use cap couples. the rectifier cap is AC oil caps??

thanks

Thomas