Help! I tried to recap my amp!

[docz]

This is weird there used to be a customs fee - not customs, but a flat fee that was charged for the customs handling. This used to be 380 NOK, but this may have been changed. I just remember this because this is why I stopped buying things online that had a value over 200 NOK. But of course rules change as times go by, so there might be new rules now. I do know that if you use DHL, FedEx, UPS or similar service they have lower handling fees, because they handle their customs in bulk.

DocZ

[Phil_S]

Docz: a little bit of knowledge...goes a long way, but be careful about conclusions. You are describing the power supply ladder. In the typical guitar amp, there is a 20u or 40u filter at the first node -- what you are calling the reservior -- that supplies the power amp.

In your Teisco, that first filter cap takes the rectified voltage from the 6X4 rectifier tube, filters it to remove ripple, and supplies the plate of the single EL84 via the output transformer.

You should probably download the TDSL from http://tdsl.duncanamps.com/ which will show you many things about various tubes. Look at the spec for 6X4 and it tells you IRect = 70ma and Cout = 40. This means you have a supply limit of 70mA for the circuit and the maximum filter cap on the tube can be 40u. A larger cap will stress the tube to a premature death.

Then, there is a 1K dropping resistor, followed by a 10u cap, the 2nd node in the B+ ladder. The resistor is there to reduce voltage and place a divider between the caps. The second node supplies the screen of the EL84, the reverb, and the tremolo. It is typical to supply less voltage to the screen compared to the plate (anode).

There is another 5K (or is it 2500.../1/2 5K is an odd notation) dropping resistor, followed by a 10u cap. This is the third node, supplying the two sections of 12AX7 in the preamp. Again, it is typical to drop the voltage in a guitar amp.

I'm not an engineer or scientist, so I can't give a good theoretical discussion on this topic. Let's just say, there is a clear flow to it, and B+ needs to drop as it moves from the power amp to the preamp.

As for exact values, 40u and 33u are close enough in a guitar amp. You won't see much difference. This amp would be about the same if you used three 20u caps. The higher value caps may give you a little more bass, and a tighter, less mushy sound. Anyway, the 33-33-10 caps should be just fine. I isn't a problem. I suggest you leave it alone.

For our purposes, there is no difference at all between 33u and 32u.

It is not a smoking gun. If anything, this combination would tend to reduce hum, not make more hum.

[docz]

Yes, this is a more eloquent way of saying what I was thinking I just used the words I found on that page.

But what puzzled me was that V2 was connected to the second 33uF cap, and not the 10uF cap and that the resistors were reversed compared to the schematic. I thought maybe since that page said that the reason for the second filter for the preamp tubes was that they were more sensitive to ripple, and therefore needed more filtering. My thought was that maybe someone had modded this amp in the past and put it back wrong, thus inducing the noise I am hearing. It was just a stupid thought I realize that now. In the quest for knowledge I tend to make a lot of assumptions along the way - but given time and experience I almost always find that my assumptions were all wrong

DocZ

[Aurora]

Cornelius, Doc..
there's usually no customs fee on electronic parts, but we still pay the blasted "NRK-avgift", on all electronic units that can be used to record or reproduce official norw. broadcast, - meaning amps, recorders, loudspeakers etc. This is now a unity fee, from a few ten'ers to several hundred kr's.... up until sometime mid 80's it was 17.6 % with the old 20% VAT on top!

As for the clearance fees, it may seem like some of these "vulture" co's like UPS, DHL and the likes have reduced their fees. I got some hefty surprices when the new regime was introduced about 10 yrs ago.
Professionally I regularly order eqpt from abroad, from cheap to very expensive, but we use customs brokers these days, so I rarely see that part of the invoice. The company I work for also have partial excemt from customs and VAT... pity I can't "abuse" that for personal use

[Phil_S]

If you reverse the positions of the dropping resistors and return it to the way it is on the schematic, you will raise the screen voltage on the EL84. Since the screen draws maybe 7mA of current, that's enough probably to hear a difference in the tone of the amp. Try it and see if you like the result.

I am sorry that you guys in Norway pay so much in taxes. It takes the fun out of stuff like this.

[docz]

Thanks Phil, I'll try that.

Yeah taxes are high, but at least school and health care is almost free But enough about politics, let's get back to the amps

DocZ

[Aurora]

Well, there are a few local state taxes in the US as well... a few percent??

Let's just pay and be happy......

[malt]

Hi, I have some parts fore you doc 1. pio 0,047uf, 2-mallory 150 0,0047uf+1-0,022uf , 3-sozo 0,01uf and 2- 100 ohm 1watt cf resistors send me a pm whit your address.

Elfa is ok for parts but they are little pricey, if you want to by stuff from Rs http://no.rs-online.com/web/ you can get it from Kompotek in Haugesund http://www.kompotek.no/. Chassis and trafos you can get at valvepower http://valvepower.co.uk/chassis.htm

[docz]

Would this thing work as an OT for that vibro champ?

http://docs-europe.electrocomponents.co ... 326477.pdf

DocZ

[Aurora]

Elfa is ok for parts but they are little pricey....

Well., - I don't know... most scandinavian suppliers for the professional small market are higher than their US counterparts, and so it most of their UK counterparts, too. Tubetown and Tubeampdoctor in DE are also a bit pricey compared to US...

www.ampmaker.com in UK seem sto have some nice low powered kits, but I don't have the foggiest idea of the sound....
"I'm just the piano player........."

[Phil_S]

Would this thing work as an OT for that vibro champ?
http://docs-europe.electrocomponents.co ... 326477.pdf
DocZ

I don't think so. That one has a turns ratio of 10:1 (they publish the voltage). I think you want an OT with a 5K primary. With an 8 ohm secondary, that is a turns ratio of 25:1.

How to figure the turns ratio? Square root of the primary impedance divided by the secondary impedance. Sqrt(5000 / 8 ) = 25.

Also, for a single ended OT, it needs an air gap to prevent core saturation. That is another reason why the item isn't right.

I realize this is not an item you will come by in Norway easily or for a good price, but it is a good example of what you should get:
http://www.magneticcomponents.net/Fende ... rmers.html Model 40-18030 about 2/3 of the way down the page. Or this one: http://www.hammondmfg.com/jpeg/125BSE_B.jpg

[docz]

So this one would work?

http://cgi.ebay.com/Vintage-Style-5W-Ou ... 3ef751cc3d

DocZ

[docz]

What sort of tools would I need to make those nice turret boards? And does anyone know where I might get a hold of those in Norway?

DocZ

[Phil_S]

Yes, that eBay transformer is the right one.

As for turret boards, these are made from a Fiberglas material, G10, FR4, that sort of stuff. When you drill these, the dust needs to be controlled because it is carcinogenic. Once you breathe it in, it stays in your lungs. It also dulls regular drill bits rather quickly.

Do yourself a big favor and get someone else to take the health risk. People who make these should be using a mask and a vacuum collection system.

When I drill mounting holes in these boards, I use a variable speed drill and keep it turning very slowly so that I don't have airborne dust. I watch for the small shreds to peel out of the hole. It would take forever to drill enough holes to make a working board and I remain convinced that it is too much of a health hazard. There isn't much I don't do on my own. This is one job I don't do.

If you must know, look here: http://www.hoffmanamps.com/MyStore/perl ... =223756800

[docz]

Does it have to made of fiberglass? Can't it be made from fibreboard, wood, or any other material?

DocZ