peavey Iron

[larsvictor]

Sorry Marcus,

I know it´s sometimes hard to imagine a layout just by a description.
I don´t know if there exists an online tool for layouts.
Maybe things become clearer with a schematic...

2 ways to implement a BIAS circuit with your PT.

Lars

[Aaron]

Has anyone tried the bias circuit that HAD used in ODS #121. Instead of grounding the negative side of the rectifier he uses it as the -Ve bias supply.

[martin manning]

Has anyone tried the bias circuit that HAD used in ODS #121. Instead of grounding the negative side of the rectifier he uses it as the -Ve bias supply.

Is there a schematic or gut shots around somewhere?

[martin manning]

...I could do with seeing what that would actually look like on a layout so I could make a board :D

Pretty simple mod to the board as Taylor drew it. Of course you could use just one eyelet for the ground side of the bridge.

[Aaron]

Is there a schematic or gut shots around somewhere?

This is the block diagram that was in one of the Aspen Pittman books

[norburybrook]

...I could do with seeing what that would actually look like on a layout so I could make a board

Pretty simple mod to the board as Taylor drew it. Of course you could use just one eyelet for the ground side of the bridge.

THanks Martin,

so is the first cap on the power board the smoothing capacitor for the rectified voltage then?

and..........

on the peavey schematic there's a 0.01uf 1Kv cap, which I presume is a little ceramic, across the center of the bridge. What does this do? and is it worth adding?


Marcus

[martin manning]

Yes after the rectifier the filter arrangement can remain the same. Note, however, that it would be best to up the voltage ratings of single (non-stacked) filters to 500V so their ratings will not be exceeded when you power it up with no tubes installed, The 0.01u across the bridge would be for noise suppression; might as well put it in. Some designs place one across each diode.

[norburybrook]

thanks martin, yes thinking about it I think the precision power supply rectifier board has them.

Much appreciated. Going to do some more reading up on rectification/transformers over the weekend just to get my head around the center tap and it's uses and effect. It's one of those areas I've given little attention to as building from a layout/schematic with the correct components doesn't actually make you think about the details of what's going on

M

[martin manning]

Has anyone tried the bias circuit that HAD used in ODS #121. Instead of grounding the negative side of the rectifier he uses it as the -Ve bias supply.

Is there a schematic or gut shots around somewhere?

This is the block diagram that was in one of the Aspen Pittman books

Interesting, thanks... I'll have to look in the Pitman book for that. It's just a FW rectifier with the bias voltage taken from the HT (from both sides of the HT this time) as in other schematics. Note there is an error in that circuit: The two 30uF polarized caps are reversed.

[Aaron]

Ahh, so it is! I'd forgotten I built an amp with a similar setup a year or two ago. I believe the later amps used this design.

Aaron

[norburybrook]

Yes after the rectifier the filter arrangement can remain the same. Note, however, that it would be best to up the voltage ratings of single (non-stacked) filters to 500V so their ratings will not be exceeded when you power it up with no tubes installed, The 0.01u across the bridge would be for noise suppression; might as well put it in. Some designs place one across each diode.

yes good point. I couldn't find 220uf 350v axial caps anywhere...ended up having to get 220uf 500v caps from a boutique UK supplier........cost me nearly $45 for two caps with postage!!!!!!!!!!!!

Sprague high voltage axials over here are going for over $25 each!!

crazy...


M

[martin manning]

You can get F&T, no? TAD has 220u 350V.

[norburybrook]

You can get F&T, no? TAD has 220u 350V.

I've never been to that site before Martin so didn't know it existed!!!

Damn.....that could have saved me $30 ...hey ho...

I've found a new parts source if nothing else!!!


you've still got it lucky over your side of the pond though regarding all this tube stuff

while I'm ordering parts and have your attention, what would be your ball park guess in regards to dropping string values for this build I think the rectified voltage on the Peavey schematic is 508vDC so quite a bit above the twin transformer voltage so I'll need bigger values to get it back to somewhere resembling the specified wonderland values.


Marcus

[larsvictor]

Marcus,

then you should know this site too: amptone in poland !

They are not expensive. A 220µF@300V for 6,16 € + shipping.

https://amptone.pl/p/21/214/220uf-300v-axial-.html


Lars

[norburybrook]

Marcus,

then you should know this site too: amptone in poland !

They are not expensive. A 220µF@300V for 6,16 € + shipping.

https://amptone.pl/p/21/214/220uf-300v-axial-.html


Lars

thanks Lars, this is all great stuff. much appreciated

I can now spend more time browsing the interweb looking for parts....


This is becoming quite addictive....


and I've got a KEMPER..............



I've decided to got turquoise suede with black vox for the new build in honor of John Mayers current SSS favorite

found a pig skin suede hide on ebay here in the UK.

I've also traded one of my mic's for a router......

all I need now is some spare time.....I've suddenly become in demand.......which is a good thing in the music business

one of the last projects I worked on is top 5 in the album charts.


M