Newby first build amp 832.

[andrew ivimey]

Oui, pourquoi mon brave?

eh bien mes amis, after an excursion to 6C41 and even a quick detour back into 6C33 land I realised (yet again) that if you want power you have to put up with vast appalling amounts of heat. There may be a magic ssppot where all is nicely in balance and the heat is minimised but cripes! what larks. Yeah and well not really.

So I thought a bit and thought a bit and at last I came back to 832 as PSE with SRPP 6SN7 front end. 270volts HT and 5K output trafos.

It is a timid beast (i.e. can't cope with track 4 of David Gray) but there may be something to it. A few odds and ends need a good tidy up.

It is not a great amplifier (yet! ha ha) it has shall we say, 'character'

cost approx £100 all new components - how much shiraz is that?

bon voyages!

[kuroguy]

At last I get a look at your 832 amp. Looks nice. I used the connectors from an old ATX computer power supply and a couple layers of heat shrink tubing to make the connectors for the plate pins on the 832s. They fit perfectly.

[pre65]

Hi-strangely enough i have a "knackered" ATX power supply so i will be looking to mod my connectors.

I spent ages looking for anode connectors and croc clips were just expedient !

Since the picture was taken the output transformers have been replaced with Audionote ones (the Hammonds are having a "holiday" in Yorkshire) and i have put a switch in the feedback circuit.

Most of the time i listen without feedback.

I really like the sound of this amp and apart from a minor hum problem it is all i could ask for.

It even drives my KLS 3 to great effect,although in doing so runs a bit warmer than with the VoFos,or Adires which must be easier loads.



Philip

[andrew ivimey]

If you carefully remove some pins from an el34 type socket all you need do is solder anode wires on and cover with shrink to fit cable - works a treat with these cheeky 832s!

If there is some residual hum, I'd blame the HT. There is only a massive cap. I'd add a choke. I know push pull amps appear not to need so much smoothing for obvious reasons but ...

I have been tearing my hair out over a 6B4g Push pull amp where a 417 drives the output pair through an interstage. Initially (using a regular CLC valve power supply,) it sounded very promising. So I got on with the real build using a voltage doubler for very long winded tedious reasons. Hum.

So bu''e# it! I added DC on the filaments. It helped but ggggrrrrrr. So I plonked a 10henry 350ma choke in amongst the PSU and ... close to silence. But the interstages I used are **** so the whole project has gone onto a back burner. Hammer or new interstages!

Anyway, having a reliable and powerful choke around is interesting to be able to switch in switch out to see what is happening, ripple/noise/hum wise. I know MJ has pages on determining the use of a choke but he makes me nod off into my cocoa too easily.

[pre65]

Hi-i did think of "upgrading" the power supply using the 200-0-200 transformer as 400v with a valve rectifier and chokes etc but that would really mean a major rebuild.

I will see how i like the PT15 first !

If the PT15 work as i hope that will give me some time to "play" with 832 and reincarnate into a mk 2

Perhaps one day i could "play" with an 833.


Philip

[kuroguy]

Originally Posted by pre65

... and croc clips were just expedient !

and dangerous. you should definatley insulate those high voltage connections

Originally Posted by pre65

...I really like the sound of this amp and apart from a minor hum problem it is all i could ask for.

Mine is dead silent without any chokes, just a couple of diodes and one big capacitor. By the way, I used a 12 gage copper wire for a ground bus, not star grounding.

[pre65]

Hi-i used a bridge rectifier and 820uf cap on each channel,fed by the two 200v secondarys from the toroid.

In the end i kept the bus bar earth system and i did the pseudo centre tap mod on the heater supplies.

On Nicks advice i have re-done the PT15 filament supply with shottkies so i may use the old ones for the 832 12at7 valves.

I have no pets or children etc to electrocute but i will look at the safety aspect next time the amp is replaced.

I might go in for a bit of single endedness soon,300b or 45,nice to have the choice.

[kuroguy]

could you repost the picture of the bottom of your amp? I'd like to see what the competition looks like.

[pre65]

Hi-i didn't have a completed underneath shot so i took a new one.

http://i111.photobucket.com/albums/n...underneath.jpg

I dont like the way i built it underneath but it works,so will stay as it is for the moment.


Philip

[kuroguy]

Not that I have lots of experience here, but maybe a few pointers....

first, it looks like you used the same gage wire for the ground bus. Next time use heavier wire for the bus. remember, the heavier the wire, the less resistance. It will help reduce potential differences between grounding points. Second, get rid of those screw terminals and use solder type terminals. They don't come loose and have a much lower resistance to them. The last trick I know is to try to make all wires cross perpinticular to each other. this reduces stray capacitance to maintain the high frequency signals and also reduces the liklihood of inducing noise into adjacent wires. Keep the wires as short as possible as that reduces the number of times wires cross.

A neatly wired amp is a quiet amp.