letterbeacon

Re: EF85 Compressor from scratch
« Reply #40 on: September 06, 2018, 05:47:30 AM »
Thanks Letterbeacon,

Yes, it's fixed with pop rivets plus washer.

The short answer is it's time consuming ???

You have to mark the outline as accurately as possible, then find the 45 degree spot for the drill to radius the corners.

I drill up progressively getting larger and push over to correct any misalignment until it reaches the line.

Best
DaveP

Then I cover the parts I want with masking tape and jigsaw to 1 or 2mm up to the line.  Then its all down to filing to the line.

Finally I wrap the file with emery paper and smooth it all off.  Sometimes I polish it with a rag wheel afterwards.

Thanks Dave. My metal-working skills leave a lot to be desired so this is very useful to know.


DaveP

Re: EF85 Compressor from scratch
« Reply #41 on: September 09, 2018, 05:26:55 PM »
Got on well with it today.

The main part of the chassis is finished and major parts fitted.



I made the RH side panel to keep it all rigid and attached the left side of the power supply section.

All the tubes seem to fit in OK along with some 15k:600 OPT's.

There  are three sections on that chassis, regulated power supply, Compressor amp and feed forward side chain amp.



Next job is to sort out the earth busbar and the the tube heater supplies.  I will then be able to run the heater supply to the tubes and determine the value of the Al clad dropper resistor.  This has to be fitted before I can fit the rest of the power supply together.

All for now

DaveP
Soundcloud: Delayed Action.

L´Andratté

Re: EF85 Compressor from scratch
« Reply #42 on: September 10, 2018, 05:15:06 AM »
Thanks Dave. My metal-working skills leave a lot to be desired so this is very useful to know.

+1
I am planning out construction of my first real tube preamps (two of ruffrecord´s Classic Solo but  without pcb). I want to make them as old school as possible (except the rectifiers), so I have the search engine running hot on DaveP threads... ;D

Sorry for OT:
Are those Danbury transformers? Is it possible to get these screw-on shields somewhere? I use one for power supply and already know there will be hum if I go internal supply (preferred but not decided) and those should help a bit, right?



Strictly amateur since 1973...

DaveP

Re: EF85 Compressor from scratch
« Reply #43 on: September 10, 2018, 11:17:10 AM »
Quote
I want to make them as old school as possible
Well watch the next few posts carefully.

Quote
Are those Danbury transformers?
Yes, they were made especially for me by the guys who used to be at Danbury transformers.  They are not power transformers.

They were designed to be shielded input transformers and those covers were the smallest they could find.  But they are so beefy, it's possibly to use them as push-pull output transformers for 6SN7 type tubes.

Regarding your project, use toroidal transformers wherever possible, oriented with their axis at 90 degrees from other transformers and you should be OK.  Older "EI" transformers should be avoided  with "in the box power supplies", no-one wants vintage hum levels in the cause of authenticity.  Some old vintage designs have S:N levels of only -45dB.  No need to use a choke any more when you can get 12000 hour 180uF  or more caps.

Good luck
DaveP
Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #44 on: September 13, 2018, 02:05:15 PM »
The earth busbar is now finished and in place and so is the DC heater wiring.  You don't have to worry about wire dress like you do with ac twisted pairs.



I have also fitted lots of Tag strips, you can't really calculate beforehand how many will be required, so best to make sure there are plenty spare to give you the most options for the layout.



The 12 tubes seem to fit OK, I used B7G pentodes to save space, along with a 6AL5 and a 5651  voltage neon.

I will wire up the input socket before I fit the input transformers.

Now to light em up!

DaveP

Soundcloud: Delayed Action.

Re: EF85 Compressor from scratch
« Reply #45 on: September 13, 2018, 10:11:31 PM »
Just WOW, respect!  :o
www.kontrast.in - I make websites and stores online.

EmRR

Re: EF85 Compressor from scratch
« Reply #46 on: September 13, 2018, 11:03:50 PM »
Looking good Dave!
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Re: EF85 Compressor from scratch
« Reply #47 on: September 15, 2018, 07:46:32 AM »
As usual... f...ing impressive .

Best
Zam

DaveP

Re: EF85 Compressor from scratch
« Reply #48 on: September 15, 2018, 06:34:24 PM »
I appreciate the support especially as some of you in NC have more important things to worry about :(

I fitted the heater dropper to give the tubes 6.3V @ 4.4 A, then I was able to connect up the other half of the power supply.

The chassis is now complete bar the faceplate.



The input is now wired so I fitted the Edcor IPT's,  the balance pot and the voltage regulator pot.



This compressor is designed for line level, so there is no step-up in the IPT's, they being 15k:15k.  I used this particular TX because the frequency response is flat, some of Edcor's other types have peaks in the top end which will probably make them ring.  As you can see, this one is pretty flat where it needs to be.



I can now start adding the components and working out the layout.  Maybe I should say that this is an experimental design and I have no guarantee it's going to work as feed-forward, the side-chain will need careful balancing against the control amp. ???

Best
DaveP
Soundcloud: Delayed Action.

scott2000

Re: EF85 Compressor from scratch
« Reply #49 on: September 15, 2018, 07:32:01 PM »
Looks amazing!! Can't wait to see how it turns out and if you make any changes along the way............

What is the metal box in the top of the power supply in the pic ????


Re: EF85 Compressor from scratch
« Reply #50 on: September 15, 2018, 07:45:40 PM »
What is the metal box in the top of the power supply in the pic ????

EMI/RFI line filter at main AC input.

Best
Zam

DaveP

Re: EF85 Compressor from scratch
« Reply #51 on: September 20, 2018, 04:36:40 PM »
Here are some half-way through pics to give an idea of the point to point technique.  It's easier to mount components on turret boards, but you get much more connecting wiring with that method, which I don't like personally.  I like to keep wiring as short as possible in sensitive areas like input grids.



It looks like chaos but the lead wires of each part are carefully bent and placed in this close-up.



Looks better from this angle, I rarely do more than 2 hours in one sitting as you start making stupid mistakes.  It's a bit like a painting or a drawing, or a mix for that matter, much better to look at it with fresh eyes/ears the next day.



This is how I avoid mistakes and mis-wires, I go over the schematic with a marker after each soldering.

Most of the sections left to do are on the front panel.

On the subject of soldering:  I use a 40W iron and wipe the tip clean on brass swarf in a pot before every soldering.  You never get a dry joint that way.

DaveP

Soundcloud: Delayed Action.

scott2000

Re: EF85 Compressor from scratch
« Reply #52 on: September 20, 2018, 04:48:45 PM »
Wow..... I guess I knew it would be busy but this puts it in more perspective for sure! Nice!

What's that orange thing by the transformers???

DaveP

Re: EF85 Compressor from scratch
« Reply #53 on: September 20, 2018, 05:13:02 PM »
It's a wire-wound 100 ohm pot used to balance the current of the EF85's.

It's not connected yet.

DaveP
Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #54 on: September 30, 2018, 05:59:59 PM »
I had it all wired up ready to go....................then smoke!  then Off quickly.
Just in case anyone thinks I'm smarter than I actually am.............HT input cap wired back to front.

Said cap swollen and about to burst.


Any way, soon fixed and a salutary lesson to take more care.

All the components are now in place and voltages correct.



The dropper resistors turned out to be 680 ohms and 560ohms, they are rated at 7 watts but the first one  emits 3 Watts, I'm not sure I want that amount of heat cooking the rest of the amp.  I will try to replace it with a chassis mounted Al clad type if I can.

Now the faceplate...............

DaveP
Soundcloud: Delayed Action.

scott2000

Re: EF85 Compressor from scratch
« Reply #55 on: September 30, 2018, 06:44:37 PM »
Awesome! So weird I was just looking around several minutes ago and saw an old Hammond AO-33? chassis and thought of your project....It had 12 sockets exactly..... except only two of the 12 were 7pin.......the rest 9pin....


Congrats on the power up!!! Looks magnificent!!!!

DaveP

Re: EF85 Compressor from scratch
« Reply #56 on: October 05, 2018, 09:54:50 AM »
I've finished modifying the Meter.

It started off like the one on the left, just an ordinary 1mA meter.



I removed the cover and the faceplate veeery carefully and scanned it into MS Paint on 300dpi resolution.

I also carefully removed the white paper under the mechanism.

Then I drew the new markers and erased the old numbers.  I used the DIN numbers that I had previously copied into Word.

This is where Paint shows up problems....It crashes!

The only way around the problem is to save your work after every action, otherwise it exhausts its memory.

When it was done I adjusted it to the correct size and printed it on buff paper.

I sanded off the original paint and used almost dry PVA glue to fix the new one on.

DaveP

Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #57 on: October 05, 2018, 11:57:42 AM »
Photobucket and Tinypics have gone off line, hence no other pics

DaveP
Soundcloud: Delayed Action.

DaveP

Re: EF85 Compressor from scratch
« Reply #58 on: October 28, 2018, 04:44:15 PM »
Finally finished the front panel



This uses the same timings the forum agreed back when I made the GroupDIY 26C

I went to order more Letraset, only to find they have gone out of business!

I think I will have to get something similar from the US, from now on.

Now I only have to fit the front and make the base cover.

DaveP
Soundcloud: Delayed Action.

scott2000

Re: EF85 Compressor from scratch
« Reply #59 on: October 28, 2018, 05:14:20 PM »
Woah...Nice ! Matches your monitors......