Help! I tried to recap my amp!

[Structo]

Not sure what the L's mean.
The 1/2 I guess means 1/2 watt?

[badtweed]

Maybe I have missed comments on this in the already posted messages but,
have you measured any of the secondary voltages of the power transformer and posted their values here? Sorry if I've inadvertently missed that info.

If you haven't measured the power transformer secondary ac voltages yet, I'd recommend measuring them and posting the VAC values here if you are certain that you have the primary section of the power transformer hooked up properly first.

I'd even go so far to recommend that you remove any wiring to the secondaries first to ensure that some part of your circuit wiring isn't shorting out the power transformer's secondaries. Take photos of those wires to the secondaries prior to removing them.

Once you've established that your power transformer is operational then move on to verifying other parts of the circuit.

[docz]

I just completed re-wiring the power transformer the way that Phil said.

Here is a picture:

[img768]http://farm3.static.flickr.com/2494/423 ... bb18_b.jpg[/img]

I tested it and took some AC readings.

Primary

6.3V = 7V

110V - 0V = 120V
110V - 0V = 120V
110V - 110V = 240V

Secondary

6.3V = 7V

260V - E = 300V
E - 260V = 300V
260V - 260V = 600V

I also measured the speaker and output transformer again.

The speaker measured 7ohm (it says 8 ohm on it)
The output transformer measured 1 ohm when not connected to the speaker.

Does this give any new clues?

Also, I was wondering, if I do have to replace all the PIO caps and maybe some resistors etc. Would it be totally wrong to assemble a new circuit on a turret board? I imagine it might be a bit easier to do it that way.

Doc-Z

[Phil_S]

I did some ohm measuring on the power transformer, so here comes more silly questions.

These are not silly questions. We have a saying, the only silly question is the one not asked.

First side (where wall socket connects)

Between the two 6.3V 0.6A terminals I get 1 ohm - (the same reading I get when I connect the two multimeter probes together, not "I" for infinity)

Between first 110V and first 0V I get 33 ohm
Between first 0V and second 110V I get 1 ohm
Between second 110V and second 0V I get 31 ohm
Between second 0V and first 110V I get 64 ohm
Between both 110V I get 33 ohm
Between both 0V I get 31 ohm

Your PT is designed for 110v or 220v operation. It is as I said earlier. There is a bridge between the inner 110-0 lugs. Your connection to the outer 110 and 0 lugs is correct for 220V line voltage. It also works fine for 230V, but your secondary will be a bit higher than expected. This is not a problem. Ohms are a bit on the high side in my opinion, but this might simply be a function of the design. I am not a transformer guru.

If I understand, with the jumper in place between the inner 110-0, the measurement between the outer 110 and 0 lugs is 64 ohms.

The 0.6A 6.3V lugs are for one of three secondary windings. This one operates the pilot light. It looks to be wired correctly.

Other side

Between the two 6.3V 2A terminals I get 1 ohm
Between first 260V and "E" I get 237 ohm
Between second 260V and "E" I get 221 ohm
Between both 260V I get 457 ohm
Between "E" and both 6.3V 2A I get 1 ohm
Between "E" and ground wire / chassis I get 1 ohm
Between first 260V and ground /chassis I get 237 ohm
Between second 260V and ground /chassis I get 221 ohm

These look reasonable to me.

Between all ground "busses" I get 1 ohm

You shouldn't see much resistance to ground. If I understand correctly, this is OK.

Is it correct that there should be a connection between the different terminals of the power transformer? I thought it was bad to have a connection between phases and ground. Or is it that the resistance is what keeps it from shorting out?

On the primary, it is wired correctly. The bridge between the two inner lugs is to connect two internal windings and make it right for European line voltage.

I don't like that black wire from the 6.3v terminal to the E terminal. If this was my amp, I'd remove that wire. E is the high voltage center tap, which is grounded. I might misunderstand what the designer did here. He may have been elevating the heater supply, but I don't see it that way. Remove it. I don't believe anything bad will happen.

I also measured to see if there was a connection between pin 4, 5 and 9 on the 12AX7's and the power transformers 6.3V terminals, and my multmeter says there is. Does this mean the tubes are broken?

Base on what I see in the pictures, you should expect continuity. I think the black wire I said to remove may be part of the problem.

[Phil_S]

I tested it and took some AC readings.
Primary

6.3V = 7V

110V - 0V = 120V
110V - 0V = 120V
110V - 110V = 240V

The 6.3V is a secondary. Consider the primary is wound for 220V, you are reporting 240 line voltage, so nominally, expect secondary readings to be about 24/22 over expected or about 10% higher. This explains 7V on the 6.3V secondary.

Secondary

6.3V = 7V

260V - E = 300V
E - 260V = 300V
260V - 260V = 600V

This is good. See above on 7V, same applies to the 2A 6.3V. 260+260=520. We expect 24/22*520 or about 570v. 600V is reasonable. Real life is not perfect. I think it is safe to conclude your PT is operating properly.

I also measured the speaker and output transformer again.

The speaker measured 7ohm (it says 8 ohm on it)
The output transformer measured 1 ohm when not connected to the speaker.

Does this give any new clues?

Yes, a speaker will meter at about 75% of it's rating. An 8 ohm speaker showing 7 ohms is normal.

Your output transformer has a black wire on the secondary. Where does it go? I think it needs to be removed, but can't say for sure until I know more about that black wire. It could be a negative feedback loop, which would be OK even though it is not on the schematic. See if you can trace it. 1 Ohm is not OK on the OT secondary. Did you disconnect that black wire when you measured? You need to do that.

Also, I was wondering, if I do have to replace all the PIO caps and maybe some resistors etc. Would it be totally wrong to assemble a new circuit on a turret board? I imagine it might be a bit easier to do it that way.

What you suggest is known as "shotgunning". Total removal of the circuit is not recommended. Those vintage caps and resistors are where the tone is generated. New parts will not be equivalent in a toneful way.

Filament wiring looks OK to the 12AX7's (except for the black wire at the PT). Can you check for continuity from the underside of the socket to the top side of the socket? Your tubes should light up.

[Phil_S]

Somewhere you asked about 260-E-260. E is the center tap. I don't understand the theory here. E is grounded as a reference for the high voltage supply. The configuration is standard. Maybe someone who has an engineering background can explain it.

[jjman]

Grounding one side of the heater winding is not wrong, is it? Removing that reference will make the heaters floating, which will increase the risk of hum, no?

I would remove it but replace it with an artificial CT. But for now I don't think it's a priority.

[docz]

The black wire to "E" is going to the ground thingy (rail? terminal? I don't know what it is called, the strip of circuit board with terminals that the negative leads of the caps go to)

The same goes for the black wire on the OT.
And removing that wire on the OT didn't have any effect on the ohm measurement. Still 1 ohm.

There is continuity (if that is what it means when I measure 1 ohm between two points) on all the bottom pins and the socket holes on the tube sockets.

DocZ

[docz]

Pardon me for asking, but what is a CT?

DocZ

[docz]

Btw. Is it ok to hook up just the heaters and power it on and see what happens?

DocZ

[docz]

Just to help myself not get confused, I made a color coded version of the schematic to help me out when tracing each section in the real circuit. Could you guys check it to see if I got it right? I also wrote some questions on it, it was easier to write them on the schematic - rather than trying to explain it in writing.

So here it is:

[img747]http://farm3.static.flickr.com/2664/423 ... 3f09_o.jpg[/img]

DocZ

[Structo]

CT = Center Tap

I can't really help with that tranny but by the looks of that solder joint, you really need to read up on proper soldering technique.
I hope you won't be offended but you should practice your technique a bit.

The best thing to do to any wire is strip about 1/2" of insulation off, then if the strands are not tight, twist them tightly.
Now with a hot iron, touch the iron to the bare wire, after a few second feed in some solder from the opposite side.
Once the wire has wicked in enough solder to coat it entirely remove the solder then the iron.
That is called tinning the wire.
It helps make connections easier to solder.

So then you want to mechanically make a connection with that tinned lead.
If it is an eyelet lug like on a pot, feed the wire through, then with needle nose pliers, wrap the wire around the eyelet once then squeeze it tight so the wire is physically secure to the eyelet.

Then heat the joint, feed solder from other side of iron until there is a nice shiny full joint and remove solder, then iron.
If there is a wire end sticking out, take your small wire cutters and trim it flush to the joint.

In actuality, this happens in only a matter of seconds.
You just need to practice some.

If the joint is dull or crusty looking that is called a cold joint and will probably make a bad connection down the road if not right away.
So when soldering a joint, you don't want to move the wire or component as that can also cause a cold joint.

[Phil_S]

Grounding one side of the heater winding is not wrong, is it? Removing that reference will make the heaters floating, which will increase the risk of hum, no?

I would remove it but replace it with an artificial CT. But for now I don't think it's a priority.

I was waiting to hear from Docz about that wire. I agree with JJman. This is a low priority. Do this when you have the amp working and not before. It is generally unwise to fix something that may not be broken. In the end, it may not be necessary at all. Leave the black wire alone for now. That's what I would do.

Tom (Structo) gives wise counsel about soldering technique. Please don't feel bad about this. It takes time to learn this. I am attaching something that might help.

[Phil_S]

Btw. Is it ok to hook up just the heaters and power it on and see what happens?
DocZ

Generally, yes. Be more specific about your plan. Disconnect other wires from the PT? Which ones? Tubes in or tubes out? It's not a problem at all if there are no tubes in the amp.

If it were me, I would just plug in the tubes, make sure they are firmly seated in the sockets, and turn it on. There is one problem, however, which is your OT. If it is shorted (we think it is), it should be replaced before you attempt to power on with the EL84 in its socket. Remove this tube and keep it out of the amp until you replace the OT.

I don't know what OT requirement is for this amp. Maybe someone has one and can tell us. Typically for one single ended EL84, we need a primary of 4K or 5K. You want an 8 Ohm secondary. A 5W rating is more than adequate. I don't know what you can get. The Hammond 125BSE or similar is good.

[Cornelius]

Hei DocZ!

Where in Norway do you live? (I'm located near Grimstad...)

If i understood you right, the amp worked for a while after a long time in storage, then it started to make funny noises.

I've seen some suggestions for modifications here in the thread, but i'd say do not mod anything yet; repair first, then start mod'ing. Since it was working for a while, there isn't anything wrong with the wiring initially.

You said that one of the preamp tubes doesn't light up; that would be first priority. Since the other tubes does light up, there's either a broken cable; a weak soldering on the filament-pins, or really dirty sockets.

Looking at your pictures, i would agree with the others; you'd probably want to practice a bit on your soldering, to avoid future problems. (No offence. )