Hello,

I hope you guys can help me. I'm currently trying to finish the TT 18 watt Marshall style combo. Not the TMB, but the one with tremolo. I had it 'ready' I thought, turned it on and nothing happened, even the light-indicator didn't turn on. I'm fairly sure about most of the work, except for the transformer wiring-part.

What confused me was the following:
- The mains transformer differs a bit from the 'old version', as it has more wires and different colourings as opposed to the lay-out and photo's from the project-page. A legend was of course provided, indicating the wires and colour-scheme, still there's some confussion.
- I'm based in the Netherlands, so I had to wire it for 230 volts, and connected the black (the first wire indicated on the legend, mentioning '0'. Not the black wire Center Tap wire, that's indicated 3,2A. This one I wired to the Star Ground) and the only blue wire (110v) to the power switch. Then I soldered the brown wire (120v) to the grey wire ('0', but not the grey-heater wire, I think...) together. As the power winding diagram indicated those are wired in series, or did I incorrectly asume this was the right way in doing it?
- The one grey wire, that would be Anodic center tap wire (100 mA), I wired to the fuse socket.
- The white and orange wire are cut off and put a heatshrink on, I left those wires alone.
- My foremost confussion is about those 3 grey wires I think, and if I picked the correct ones for their function, and didn't mix them up somehow...

As for the out-put transformer, well actually more about the impedance switch:
- When I first wired it up, I used my multi-meter on the continuity setting. I measured each outputwire (so the 4, 8 and 16 ohm wire) as seperate from each other. But now I'm measuring them as being connected to eachother, even at the three different settings of the switch. Is this how it's supposed to be? If not, then I'm confused how this came to be, as I measured them being correct at first?!?!

I tried to be as clear as possible in my description. I hope someone can help me out, many thanks in advance!

- Timothy, from The Hague, Netherlands

Okay, I did some quick measurements with the multi-meter, and gave me the following outcomes:

I kept the black comm wire on ground, and then measured at the points:
- At the blue, black and grey/brown wire I measure 235v AC. So that's good.
- When measuring the heater wires, the grey and pink one, I measure about 3,9v-4v AC, not the 6,4v as on the diagram.  At the two brown heater cables, I measure 4 mV actually... So that's strange...
- If I measure between the grey and pink heater wire, I also get the 4 mV!
- Also, the indicator light is not switching on as well.

Hi,

How is your PT hooked up on the primary side?
Do you also measure only 4mV AC(!) when you disconnect the grey/pink wires on the EZ81 and the brown one's on the first EL84 (V5)?
The black Center Tap of the 2nd 6.3Vac is soldered to GND?
The Orange Cable not connected?

Let us know...

The OT secondary is one continuous winding, so you must have continuity between all 4 wires.

Hi, thanks a lot for your replies!

Enclosed some photos of my wiring. The white and orange cable are not connected, I heatshrinked them seperately first, then together. The black center tap goes to ground. I'll try to disconnect the heater wires this when I have time, and make some new measurements.

EDIT: Excuse me, somehow I'm not able to enclose some photo's that are 300kb per file... 

Whatever I'm trying with the photo's, it's not working, sorry...

Nicht die Schnellantwort verwenden, sondern über den grünen Button "Antworten" den Editor aufrufen. Dort können dann Bilder angehängt werden.

Grüße, Dirk

Thanks again.These are the two photo's of the power-section wiring.

[Gestern]

Hi Tim,

WARNING!
Please do NOT power up the amplifier again until this has been checked and corrected!

Something about your wiring doesnt look right to me, and Im concerned that it could cause serious damage.

First of all, Im not familiar with the transformers wire color coding or the kit itself.

From the pictures I assume the amplifier uses an EZ81 rectifier tube. However, the filament connections appear to use two different wire colors, which doesnt make sense to me.

Since there is only one PINK wire, I strongly suspect that it is actually the high voltage secondary center tap, rather than a filament connection.

1.) Check the Transformer Secondary Windings
With the amplifier completely disconnected from the mains and all capacitors safely discharged, use an ohmmeter to measure:

- PINK to PURPLE
- PINK to GREY

One of these combinations should read open circuit (infinite resistance).
The other might show something around 20 - 50 ohms, possibly more.

Based on these readings, we should be able to identify which wires belong to which winding.

My suspicion is that:
- The open circuit pair: Likely the 6.3 V filament winding for the EZ81 (pins 4 and 5).
- The pair showing resistance to PINK: Likely the high voltage secondary winding, with PINK being its center tap.

If confirmed against the transformers specifications, the PINK center tap would connect to ground through the designated fuse, while the two outer high voltage wires would connect to the EZ81 anodes.

Please keep in mind: If the wiring is indeed incorrect, the EZ81 filament or even the power transformer may already have been damaged.

2. Check Primary-to-Secondary Isolation

Once the winding identification is sorted out, theres another important check:
Measure the resistance between every secondary wire and every primary wire - these are a lot of readings.

All these combinations MUST read open circuit (infinite resistance).
If you measure any continuity, something is seriously wrong, and the transformer must not be connected to mains power - period!!
Note that an ohmmeter check alone does not prove that the insulation is safe.

3. Transformer Identification

Could you please tell me the manufacturer and part number of the power transformer?
If theres a datasheet or wiring diagram available for download, Id be happy to take a look.

Until we can positively identify all the windings and verify the wiring, please do not power up the amplifier again!

Please note: Im not taking any responsibility for the above!

Best regards, 

Geronimo

[Gestern]

Hi Geronimo,

I followed both the lay-out and the diagram that was provided with the transformer... But since the lay-out differs from the diagram, it was quite a puzzle...

https://media.tubetown.net/cms/userfiles/downloads/tt-18w-layout.pdf

[Gestern]

Ah, so the filament winding for the rectifier tube supports both 5 and 6.3 volts. In that case, at least this part might be correct.
I find it suspicious that the indicator light doesnt work, this part is clearly before any transformer is involved. Just out of curiosity, did you check the fuse in the AC inlet socket?

I would definitely go through all the windings systematically, measuring their DC resistance with the amplifier disconnected from the mains, of course and all tubes removed.

The primary winding (blue to black) should read X ohms. This exact same resistance can also be checked on the Live and Neutral tap in the Power Inlet Socket. This would rule out any breaks in the Fuse / Switch chain.

The secondary windings should be checked  for continuity as well. Important is to pull all tubes, otherwise you read their filament resistance rather than the low resistance on the filament windings.

Hope this helps.

[Heute]

It's difficult to validate your wiring, especially on the PT primary, with the pictures only.
As per the schmatic you posted, your PT needs to be connected like this to the AC side:
For 230Vac In:
Black = Neutral
Bridge Brown to Gray
Blue = Phase
For 240Vac In:
Black = Neutral
Bridge Brown to Gray
White = Phase
6.3Vac Heater is Gray/Pink (I hope you did not mix up the two gray)
2nd 6.3Vac Heater is Brown/Brown with CT (Black)
HV is Purple/Purple with CT Gray (again, I hope it was not mixed with the other Grays)

just my 2c
Blues