Help! I tried to recap my amp!

[Phil_S]

That cap would likely be at least 250V. Unfortunately, we don't know for sure. I think you can put it in the circuit and see how it works. If this is in the tremolo, and it is the wrong value, it may not oscillate properly or maybe not at all.

For the IEC inlet, I don't think the existing hole is the best choice. That one comes in through the bottom of the amp. See if you have enough room to put it in the rear corner, near the power transformer. Measure carefully to check for interior clearance. You can move the blue and white filament wire out of the way. The IEC can go vertical if you have the height in the metal. It is hard to tell, how high is the rear wall of the chassis?

I am assuming that rear wall is accessible when the chassis is in the cabinet. Looking at your piccture, I see that rear wall has no holes in it. If not, then maybe your 15mm hole becomes the choice of last resort.

If you can, get the type of IEC that mounts with screws. I have been using snap-in type and really don't care for them. I have one screw mount and it is much better. You say your are a computer technician....harvest an IEC inlet from a dead computer and take the line cord, too.!

[docz]

The cap is for V1, the one that connects to V2, the other one I switched was the one that connected to the output tube.

That was my plan - to butcher an old AT power supply

The back wall however is to narrow to fit an IEC, it is only a little over 1cm high (about 1/2 inch), the front is all maxed out in terms of space, so that only leaves the bottom.

I will try figure something out, maybe I can find a vertical mounted IEC or something.

DocZ

[docz]

Ok, new cap will take three weeks to deliver. I have a lot of stuff to play with, any suggestions what I can do with all this stuff?

I have:

9x 33uF 450v Electrolytes
10x 10uF 450v Electrolytes
50x 2.2k 2W resistors
a bunch of 1/2W resistors from 1R - 3M
2x 12AX7
1x 6X4
1X EL84
12x MPF102 transistors

Maybe I can use some of this stuff to start another amp project?

DocZ

[malt]

Ok, new cap will take three weeks to deliver.

Hi doc, what cap do you need? If i have it ill send it to you for free, three weeks thats to long.

[docz]

Wov really generous, thank you very much!

I'm actually waiting for 3x.01uF and 2x .005uF and 1x .05uF but If you want to send me one it will at least get me going

DocZ

[Phil_S]

I have a lot of stuff to play with, any suggestions what I can do with all this stuff?

I have:
9x 33uF 450v Electrolytes
10x 10uF 450v Electrolytes
50x 2.2k 2W resistors
a bunch of 1/2W resistors from 1R - 3M
2x 12AX7
1x 6X4
1X EL84
12x MPF102 transistors

Maybe I can use some of this stuff to start another amp project?
DocZ

You can make a AA764 VibroChamp with these parts and have plenty left over. Get the schematic and layout at http://www.schematicheaven.com
You can use all the tubes (6X4 will work fine as the rectifier) and some of the 450V filter caps (use 33u instead of 20u, or a pair of 10u in parallel = 20u). You can probably use many of the resistors. You'll need signal/coupling caps, a chassis, sockets, transformers, pots, wire, etc. Make a bill of materials, and check it against the schematic three times. You want to do the best you can to get all your parts ordered at one time so that you only pay one shipping fee. The most expensive things will be the PT and OT. If you can find an old computer carcass that has a small case, it can be gutted and used as a chassis.

This is the perfect first build. Congratulations, you are now addicted to tube amps in the worst kind of way. There is no cure. Prepare to live with your new condition. You know the Eagles' "Hotel California"? You just checked in.

[docz]

I actually decided to do a little inventory, and I discovered all of this:

2x 12AX7
1x 6X4
1x EL84
23x 33uF 25V Axial
8x 10uF 25V Axial
19x 10uF 50V Radial
2x 10uF 63V Axial
10x Electret capsules
20++ 300pF Radial 50v
20++ 15pF Radial 50v
20++ 68pF Radial 50v
20++ 15nF Radial 50v
20++ 3.3pF Radial 50v
20++ 2.2nF Radial 50v
20++ 4.7nF Radial 50v
20++ 220pF Radial 50v
20++ 10nF Radial 50v
20++ 5.6nF Radial 50v
20++ 20nF Radial 50v
20++ 22pF Radial 50v
20++ 3.9nF Radial 50v
20++ 100pF Radial 50v
20++ 1nF Radial 50v
20++ 150pF Radial 50v
20++ 33pF Radial 50v
20++ 47pF Radial 50v
20++ 470pF Radial 50v
20++ 100nF Radial 50v
20++ 4.7pF Radial 50v
20++ 2.4pF Radial 50v
100x 220pF Radial 50v
9x 33uF 450v Axial
50x .047uF 100V Radial
2x .022uF Radial
11x 10uF 350V Axial
5x A500k Pot
5x B1M Pot
50x 2.2k 2W
50x 1k 2W
50x 82k 2W
100x 330R 1/4W
100x 22k 1/4W
100x 3.9l 1/4W
100x 10R 1/4W
10x 1R -> 3.5M 1/2W
100x MPF102
40x LM386
10x B10K Pot
40x LED White 3mm
40x LED Red 3mm
40x LED Blue 3mm
40x LED Green 3mm
40x LED Yellow 3mm
40x LED Pink 3mm
40x LED White 5mm
40x LED Red 5mm
40x LED Blue 5mm
40x LED Green 5mm
40x LED Yellow 5mm
40x LED Pink 5mm
25x Mono Jack 6.3mm

I have a bunch of old computer cases I can use for metal. I just need to buy a mallet, and a tap and die kit and I have enough aluminum to make lots of boxes. Maybe I can make some effect pedals or something as well?

I'll check that vibro champ out, it looks cool! Would that transformer I found earlier work on that?

BTW is there a place online where I can read about those filter caps? I'm not sure what dictates what values to use. I haven't been able to figure that out. I noticed that the Champ has a bunch of different circuit versions with different filter cap values. I know they smooth out the voltage, and help the rectifier produce a continuous DC current, but why one uses 40uF in circuit and 10uF in another is a bit puzzling to me.

When it comes to ordering the parts in one package, I can't do that. Because of import restrictions in Norway, we are only allowed to purchase for 30USD taxfree. Everything over that is added a customs handling fee of 70USD + 25% tax on the whole value including shipping. So things get quite expensive if I don't purchase in small packages. I haven't found any place locally in Norway that sells components, well I have found, but they are either expensive or you have to buy in extreme high quantities.

DocZ

[Structo]

Looks like you have a pretty good stockpile of parts!

Yes the cap value is chosen to work best for the frequency that needs to be attenuated or smoothed.

It comes down to capacitive reactance and R/C time constants.
Also if a choke is used the inductive reactance is also part of it.

From the Valve Wizard the formula is:

The reservoir capacitor (first large cap) can be found using:
C = (t * I) / V
Where:
I = average load current drawn
V = ripple voltage peak-to-peak
t = duration between charging cycles and is equal to: 1/twice mains frequency.
In Europe the mains frequency is 50Hz, so: t = 1/100 = 0.01 seconds.

The reservoir capacitor required will be:
C = (0.01 * 0.188) / 35
= 54uF.
The nearest standard is 47uF. This would give a 40V ripple which is 11%; perfectly adequate. Most modern designs use a value from 33uF to 220uF at most. Hifi amps may use much more, but don't be tempted to use very large values unless your power transformer is designed to handle a lot more current than you actually need. The low power-factor caused by using a huge reservoir capacitor can cause a 'borderline' transformer to overheat!

http://www.freewebs.com/valvewizard1/smoothing.html

What I do if I am trying to make a new power supply for an amp is to look at similar amps to see how they filtered the ripple and added the various nodes for B+ voltages.
So in other words, I borrow ideas from other amp designs because I am too lazy to do all the math.

The Valve Wizard site is a great one to read along with Aikens site.

http://www.aikenamps.com/

[Aurora]

Have you checked www.elfa.se
Sells small quantities by Visa or Mastercard...maybe not the very cheapest, but generally a good selection for modern electronics. Some "tubeworthy" parts.......also there's no customs fee, as they do consignment deliveries to Norway.
There's also some good ones in Germany, - www.tubetown.de and www.tubeampdoctor.de
Usual customs fee, but less postage than US.....

BTW - sent you a PM yesterday...

[Cornelius]

Doc; where did you get those customs fee from?!

The last 2 times i ordered from the US, i ordered parts for $150 and $200, and i paid around $35/$45 in customs/tax total when i picked it up at the post office...

[Aurora]

Then you were lucky! Happens from time to time....
There's 25% VAT plus a handling fee from 200-500 kr, depending on which company does the actual declaration.
In some cases there's also a regular customs fee for electronics.......

[docz]

I thought you had to be a licensed electrician to shop at Elfa. I never gave them a thought.

There is a NOK 380,- customs handling fee, at least there used to be. Has this changed?

DocZ

[Aurora]

All foreign trade from Elfa goes through national sales offices, who are the legal importers. Try calling the Oslo shop....
EDIT: all prices accessing through elfa.se/no are NOK ex vat...

[docz]

Wov, that valve wizard page says it all! Wonder why google didn't find that one for me when I tried googling all of this stuff? Shame on google.

EDIT:
Given the information I found on that wizard site you gave me, I now understand that the first cap is the reservoir cap, and the next two in line paired with their resistor is the filters. The first filter is for the power tube, and the second one is for the 12AX7s, I understand these are more sensitive - so they get a second filter right? So I thought I'd look at my schematic and my amp to see what is going on. In the schematic it says that the uF values of the caps are 40(reservoir) - 10(filter 1) - 10(filter 2) with a 1k resistor between the reservoir and filter 1 and a 5k resistor between filter 1 and filter 2. Then reservoir cap connects to the rectifier, (or the rectifier connects to the reservoir is probably more correct to say ) , then the power tube connects to filter 1 and the 12AX7s connect to filter 2. But when I check the in my amp to find the implementation of this thing I find a few differences. First the values - this I new, but I don't know why, someone told me that they might have changed it in the production line. Well anyways the values are 33(reservoir) - 33(filter 1) - 10(filter 2) (originally 32 - 32 -10 before I got my hands in there), and the resistors are the other way around, 5k between reservoir and filter 1, and 1k between filter 1 and filter 2. The rectifier connects to the reservoir, and the power tube connects to filter 1, V1 connects to filter 2, BUT v2 connects to filter 1! Is this a smoking gun? Or is it of no importance what so ever?

DocZ
DocZ

[Cornelius]

Then you were lucky! Happens from time to time....
There's 25% VAT plus a handling fee from 200-500 kr, depending on which company does the actual declaration.
In some cases there's also a regular customs fee for electronics.......

It doesn't seem to be any customs fee for electronics, according to 'toll.no'. There is 25% VAT if the total value minus shipping are above nok200,-.

And i've checked what i had to pay when i picked up the packages; it was the 25% VAT, + nok90,- for handling. The shipping was handled by usps and it's Norwegian counterpart, and the latter did the custom handling. (i think.)