Anderton '64 reissue JTM145 - any info?

[jazbo8]

Matec - thanks for the updated schematic! Fantastic work as usual.

epis - no apology needed. But it does seem a lot work to test the OPT and it would no doubt void the warranty. Wonder if we can order replacement OPTs from Marshall or Dagnall?

[Matec]

PostPosted: Fri Aug 15, 2014 12:01 am Post subject:
Sure, what do you need ? Just ask. Very Happy

If you wanted to ask how to measure impedance, it's easy, but conjuctiv filter C9+R12 needs to be unsoldered at one end and center tap of primary ( going to B+) as well.
Small AC voltage should be applied to secondary.
Primary voltage should be measured at pins 1 and 6 of the socket V3.
Output power switch must be at 1W.
That's gonna be complicated, probably transformer needs to get out of board
It would be nice to know even DC resistance and inductance of primary.
These measurements are kind of primitive, but could give an idea how OT was done.
I assume there is no complicated interleaving schema, these amps were build cheap (my opinion)
Probably to much headache for jazzkramer.
Cheers, Damir
P.S.
I would like to know the size of transformer core too.

Epis

Everything that you said is correct, but for a basic check nothing needs to be dismantled or desoldered.

My idea is this:

Connect the secondary of a transformer low voltage (6.3V or 12V), the internal connectors, SPKR +, and SPKR-. These are connected to the secondary taps of 16ohms.

And measuring the voltage that appears between pins 1 and 6 of the valve V3. And also the connectors SPKR +, and SPKR-

Cautions:

Remove all valves
Disconnect the amp power transformer completely.
Make as few measures in these two sets of points: SPKR +, and SPKR-; and then pin 1 and pin 6 (V3)

It is essential that the rear Power Switch is set to 1W!

The meter should be set to "AC voltage".
Pins 1 and 6 the expected voltage should be between 200VAC and 450VAC, so care is needed! The range of voltages, the meter must be at least 750VAC.

Measurements of voltage SPKR +, and SPKR- should be made to the scale of meter in 200VAC, soon after, the other measure, this will provide a little more precision measures.

I also put a low wattage bulb in series with the transformer test, to prevent any "accident"

At low frequencies such as 50 Hz or 60Hz, the conjuctiv filter, will not have a remarkable performance, I do not think that needs to be disconnected.

If anyone has any more suggestions or have any comments, please do.

Do not want anyone to get involved in anything that would bring physical or property damage.

Even more.

PS Today I'll be out a while, so if there are any more questions, just post the answers tomorrow.

Matec

[jazzkramer]

Hi guys, Sorry, I can't unsold anything on the board because the JTM1 I have is not mine and I don't want to compromise the warranty or worst, damage it. (And I don't find my solder, here I'm a host, my home is 10K km far from here).

I don't have any AC transformer, but maybe I can do something different:

Listen and tell me what you think:

I have a "CD audio test" with many audio pure sine waves.

1) I could play for example a 1000 hz sine wave by a CD player, measure the line out of the cd player by AC tester so we know the actual precise AC RMS voltage.

2) connect this line out to the secondary transformer (SPKR+, SPKR-)
than measure by tester the primary transformer out (Pin 1 and 6 of V3),
so we know the AC RMS voltage of the primary.

(I know this voltage can be very high, I will be careful)


I will do this after removing tubes and after removing all external connection (power, lamp) from the board.


The disavantage is that the voltage of a cd player is low (so measurements can have more errors even if I use the appropriate tester scale)
The advantage is the voltage is low and at a higher frequency, so I think is really difficult I could damage the board.


Could this be good?


OR: METHOD 2: I DON'T HAVE A SPEACKER, BUT If I found one:

1) I could play the cd player sine wave in the JMT1 input
2) measure AC volt at V3 Pin 1 and 6
3) measure the AC volt at speaker out

We have this way a votage Ratio as well.

(the main problem is I don't have the speaker to run the JTM1 at 1W and I could only run it at 0.1W because it can be used unloaded at this power, that is actually 0.22 as stated by the engineer who projected it).


Bye, jazzkramer.

[Littlewyan]

I think I'm going to have to order a new Power Transformer for my amp guys. With my current transformer giving me a B+ of 340V I can't run the valve too hot, which means I get some crossover distortion and I get a LOT more headroom. Thus not very much distortion. So I think I'll have to order a new PT so I can run a lower B+. I've found one which gives 200VAC on the B+ Secondary so that should be about 270VDC. It can also take more current which means I'll be able to try different valves.

What do you think?

[epis]

Hi Littlewyan, I would say go for it ! I'm interested as well to try out other double triodes in output. I did try already 12ax7 and 12at7, I didn't like them. 12AU7 is really good.

[epis]

About testing the OT in the amp, my main concern was ground connection to both primary and secondary. If we used small AC voltage at speaker output, high voltage on the primary of OT would find the path to the ground trough center tap, and B+ filter caps.
Here is another method, it could work well, but they are using 1kHz/1V AC sinusoidal signal hooked up at primary.

http://www.marstran.com/Measuring%20Pri ... edance.htm

Jazzkramer, what type of multimeter do you have ?
Can it measure 1kHZ AC voltage ?

Cheers, Damir

[jazzkramer]

Sorry guys, I have some unespected problems in these days, I'm late with all the jmt1 test and schema check, I will do as soon as possible

Bye, Jazzkramer

[jazzkramer]

Hi guys,

I almost checked all the board. Matec you are great, the last schema seems correct. The diodes bridge has different names, but it's the same I mean,
if you want, in your schema from top, the first is D4 the second D2 the third is D1 and the forth is D3, the fuse is not in that position but it's between the diode bridge connecting D4 and D1 to the transformer.

Ok, a part from that, I have BIG problem checking the output part, after the output transformer, this because many connection has ZERO ohms between them, probably because the transformer has ZERO resistance with some impedence, but the tester does measure real part of impedence resulting in zero ohm.
MAybe for that I could not well identify how the switch do work (I mean which contacts it connects or open).
Not all the tracks are clear becouse they are under the output jack and output transformer.
The transformer itself has many pins and I can not identify them...
So, don't know how to do.

About the measurement of the transformer, actually, I know the owner is not very happy about that and, becouse I'm not sure about what I'm really doing (I mean I'm a little worried maybe damaging it, I don't know...) maybe I will not try to. Don't know, have to think about.

Ok, at the moment this is the "result". In the weekend I will test all resistors values by tester and by colors. So we can be sure about that.

Only remains the output schematic unsure and the transformer datas.

Bye, jazzkramer.

[Matec]

While not enough information about the amps, of course I could not help but try here, the values ​​"discovered" by us in these last days.
How changes involve the question of personal taste, no mods or opinions in this text that should be considered as a type of rule. But for me they serve.

The first changes I made to my amp was add the capacitor C1, I had no idea of ​​the result, so when I heard, it was excellent, he raised a bit the exit sign in the middle and high frequencies. But the conjunctive filter has been acting more and offset the treble.

The next step was to increase the value of the capacitor C9 conjunctive filter itself, which softened the treble. Before this change made ​​the sound dull. Now improves response and does not let the sound with the appearance of fry in treble sounds with distortion.

The change of capacitor C6 10uF to 1uF increased over the mids and treble, leaving the bass further. But it makes that sound is not confusing, the bass, with drive. It took a while, but in the end I agreed that there was improvement.

The R9 resistor in my amp was 560k, but it was seen that was worth 56k, was tempted, but after many tests I refused. The sound became "skinny" without bass, and got shrill treble. I did not like. Won the 560k.

The capacitor C108 brightness. Was 470pF. Stood at 220pF. To my Fender improved. Maybe a Gibson needs more shine.

The 100pF capacitor C19 was changed, did not notice significant change, so he stayed.

C24 was to 1uF, I carelessly was keeping him in 0,68uF. This value only for JCM1.


I also tested the "CS JTM145 kit" inserting C8 and C13, but not liked, at least not on the same circuit with C108.

Cheers

Matec

[jazzkramer]

Hi Matec,

I think in the 145 there's C12 is added as well near the output jacks, of course I don't know the value.

Bye, jazzkramer.

[Matec]

OK

Build already shown us that value in the list is that he did, C12 = 3,3uF 100v.

If as in JCM1, this component is in parallel with R18, and part of the attenuator circuit 1W / 0.1W.

Matec

[Littlewyan]

I changed my tonestack to 33k/470pf, changed R31 to 820R and C108 to 4700pF. I also added C1, changed C6, C9 to JTM1 values and like the sound very much. I think the key ingredient was the 4700pF bright capacitor as this really brings out the upper mids when the volume is on 8. It also gives the amp a really aggressive 70s Marshall tone. I tried adding C13 but it was too much. As the 12AU7 doesn't have much low end I don't think it misses the presence control.

[jazzkramer]

Hi guys, just checked all resistor values, even if was probably already known. I checked by tester and I copied the colors. N.B. 5 colors resistors may have color spelling reversed (becouse I don't know the color code without checking).
Some of the resistors result in ZERO ohm by tester, but I think it's because of the schema sucking tester current.

R1 yellow purple brown gold 468 Ohm
R2 brown green brown gold 149 Ohm
R3 brown orange black black brown 99.5 Kokm
R4 brown orange black black brown 99.6 Kokm
R5 brown orange black black brown 99.5 Kokm
R6 brown orange black black brown 99.6 Kokm
R7 yellow purple red gold 4.65 Kokm
R8 brown brown black purple red 2.68 Kokm
R9 brown red black blue green 56.2 Kokm
R10 yellow purple black orange brown 470 Kokm
R11 green blue orange gold 55.6 Kokm
R12 brown black orange red 9.88 Kokm
R13 yellow purple black gold brown 47.4 Ohm
R14 brown gold black red grey 0 ???
R15 brown black black yellow brown 1 Mohm
R16 green blue orange gold 55.5 Kokm
R17 brown black yellow gold 99.1 Kokm
R18 brown grey black gold 0 ???
R19 yellow purple red gold 4.65 Kokm
R20 brown green black brown brown 1.49 Kokm
R21 ABSENT
R22 ABSENT
R23 brown black yellow gold 99.4 Kohm
R24 ABSENT
R25 ABSENT
R26 brown black yellow gold 99.2 Kohm
R27 brown green black brown brown 1.5 Kohm
R28 brown black black brown brown 1 Kohm
R29 brown black black yellow brown 1 Mohm
R30 yellow purple black orange brown 470 Kohm
R31 brown green black brown brown 1.5 Kohm
R32 brown black blue gold 10 Mohm
R33 grey red black black brown 813 Ohm
R34 brown black black yellow brown 1 Mohm
R35 brown black black blak brown 0 ???
R36 yellow purple black yellow brown 4.62 Mohm

[Matec]

Jazzkramer.

Thanks for doing this work. His lecture showed some more values ​​that were not right. I saw that the values ​​of R32 and R35, were not correct. And will be fixed soon, the colors R35 must be 100R.

Already R13 and R18 respectively have the values ​​of 82R and 18R. To measure the values ​​correctly, just keep the key power in 1W.

Thank you.

Matec.

[jazzkramer]

Hi Matec, I think I tried with the 1W and with the 0.1W setting and it was always ZERO. I forgot to put a jack inside the two speaker out so, maybe they were connected to the mass... don't know. I remember trying to check your schema in this section I had various problem: my tester is not respondig correctly in this part.

I now had to give back the head to the owner, so I can not do any other test.
Sorry for the Output Transformer thing too. I think We need to find an owner to do the test.

I'm sorry Build is not with us, I would really really liked to have the 145 tone board and input board schematic...



Bye, jazzkramer.