please help my JTM45

[kwm488]

hi
i just finished to build a JTM45. but this amp is not work . the amp no guitar sound after i plug guitar to amp. but i can hear the amp little noise sound when i adjust presence . i sure my amp wiring is correct, i check it three time.

the voltage is
B+ 450v
KT66 pin 3,4 and 6 is 450v , pin 5 is -46v
V3 pin 1 is 250v , pin 6 is 230v
V2 pin 1 is 180v , pin 6 290v
v1 pin 1 is 340v , pin 6 is 340v

but i think V1 pin 1 and pin 6 voltage too high, is it not correct

and i use mulitmeter to check the V1 pin 1 voltage. i hear noise from speaker. and one of KT66 is flash one time.

now, i can't hear any amp noise even i adjust the presence.

i hope to get suggestion , i am no idea now

and my amp use MM RS PT and OT. this amp no HT fuse. so will my OT dead? how can i check it?

thank

[kwm488]

[sluckey]

but i think V1 pin 1 and pin 6 voltage too high

I agree. But we need to know the voltages on pins 2, 3, 7, and 8 also.

[kwm488]

sorry, i forget to write down . but it is normal.

[tubeswell]

You have a lot of long runs of wire in there, and it could well be confusing you as to what is going where. I suggest you shorten all the leads as much as possible, then you will have a clearer image about where you have gone wrong.

As to what caused your amp to fail, I'm guessing it could be miswiring somewhere (like wrongly-connected tube socket pins), or a short from the B+ to ground (seeing as how you mentioned arcing/flashing in one of the output tubes) - either through a filter cap or a tube, or even a wire from the B+ touching the chassis. You will have to check everything for shorts.

[kwm488]

Thank

I will cut the wire. Btw, it is come from ot , I can choose how many k in ot primary . So I can use 6l6 el34


Will check the wire connection and b+ short problem. Right now, the amp is no sound totally. Will my ot is dead, because this amp no ht fuse. But the check the resistance of ot primary center tap to the wire which connect to power tube, it is not more than 1k.

I really hOpe to know what happen if b+ short but no ht fuse

Thank

[Willabe]

The OT primary (side that goes to power tubes) resistance (I think) is usually less than 100R from one side to CT, for a 2 tube OT .

Measure each side to CT to see how close they are to each other.

Are you using a lamp limiter at start up to see if there is a short? Here's a link to how to make and use one. This is a must have tool.

http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf
                      

                                     Brad      

[Willabe]

I have a Hammond OT (1650R) 100w/5000R CT for 4 power tubes.

1 side to CT reads 53.7R, the other reads 46.5. I think if this OT was for 2 power tubes the resistance reading would be about double per side.


                                    Brad    

[tubeswell]

But the check the resistance of ot primary center tap to the wire which connect to power tube, it is not more than 1k.

That won't tell you much about whether its shorted I'm afraid (and the DC resistance across transformer windings is usually pretty low in any event). You need to disconnect the PT secondaries from the circuit and (carefully) connect the primary to a wall voltage and (carefully) measure the VAC across each secondary (measuring from the CT to each end where the winding has a centre tap).

For an OT, you similarly need to connect the primary to a VAC voltage and (carefully) measure the secondary winding (/taps) VAC.

A shorted winding will show up as no VAC, and a partially-shorted winding will show up as lower-than-expected VAC.

[kwm488]

hi
the result is 78ohm and 69ohm for the OT center tap to both side. and i test all preamp tube, all correct. and i sure all B+ wire haven't short to ground.

[kwm488]

i use this small speaker solder in JTM45 output. and i find out this speaker is dead, so i can't hear any noise even i adjust presence. now, i plug it to my marshall cab, i hear the noise . i think this mean the OT is not dead.

in the other hand, it is no guitar sound too. and even i turn the amp volume to max, i think the noise is not too serious. but in my twin reverb, if i turn the volume to max, noise is serious

[kwm488]

Hello. I guess two reason of nO sound problem.

Because volume through presence is work. I guess maybe input jack problem, but I sure it is wiring correct.

Another is v1 problem. Can anyone tell me is v1 plate voltage of 340v is problem?

[sluckey]

Another is v1 problem. Can anyone tell me is v1 plate voltage of 340v is problem?

Read reply #2!

[kwm488]

The other pin voltage is same with follow

[LooseChange]

If V3 is the Phase Inverter, you should have around 30v (estimate) on pins 2 and 7.

[sluckey]

If V3 is the Phase Inverter, you should have around 30v (estimate) on pins 2 and 7.

Yes. Measure those voltages again and tell us what your meter says. Don't point to someone elses voltage chart.

I still think the high voltage on V1 plates is a big clue, but let's do a simple check to eliminate the PI and PA section. Turn all 6 knobs to 10 (max CW). Now put a meter probe on the center lug of the TREBLE pot and touch the metal probe tip with your finger (this is safe). Do you hear a healthy buzz through the speaker while touching the TREBLE pot center lug? Next put your meter probe on the center lug of a VOLUME pot and touch the metal probe tip with your finger. Do you hear a healthy buzz that's even louder than the TREBLE pot test? Next put your meter probe on the center lug of the other VOLUME pot and touch the metal probe tip with your finger. Do you hear a healthy buzz that's even louder than the TREBLE pot test?


Now for V1... Look at the V1 tube Can you see the filaments glowing? Now turn the amp off and make some resistance checks. First check each plate resistor for V1. Just put your ohm meter probes directly across each resistor. What are your measured values? Next, put one ohm meter lead on chassis ground. Connect the other lead DIRECTLY to V1 pin 3. What is your measured resistance? Repeat for pins 2 and 7.

In summary, here are the measured numbers I want you to report...

Voltage on V3 pin 2.....
Voltage on V3 pin 7.....
Resistance across V1 pin 1 plate resistor.....
Resistance across V1 pin 6 plate resistor.....
Resistance between V1 pin 3 and chassis ground.....
Resistance between V1 pin 2 and chassis ground.....
Resistance between V1 pin 7 and chassis ground.....

And answer the TREBLE  and VOLUME pot check questions.

[rafe]

That speaker looks just a tad small to handle your amps power or even the lack of it . I sure hope the other members can supply you with the help you seek......

[kwm488]

Hi

I do a test. I turn all knob max. And I use meter one side to touch center lug of volume 1 ,2 and treble. Hiss noise when I touch volume 1 and 2. But no response on treble. But I sure treble is work.

And all resistor value correct.

I try to use meter test the pin voltage. When I touch the v5 pin 3 . I hear vibro noise. But no vibro noise in v4 pin3. And I try to use meter probo touch v5 pin2 more second. It kill my meter.

Why???????

[kwm488]

and all tube is light up when i turn the amp on

[sluckey]

I do a test. I turn all knob max. And I use meter one side to touch center lug of volume 1 ,2 and treble. Hiss noise when I touch volume 1 and 2. But no response on treble. But I sure treble is work.

Did you touch your finger to the metal probe tip like I asked???

And all resistor value correct.

I specifically asked for five measured resistance values. I even laid it out so you could easily reply. I EXPECT FIVE NUMBERS FOR RESISTANCE MEASUREMENTS. AND I WANT TWO NUMBERS FOR VOLTAGE MEASUREMENTS.

I try to use meter test the pin voltage. When I touch the v5 pin 3 . I hear vibro noise. But no vibro noise in v4 pin3. And I try to use meter probo touch v5 pin2 more second. It kill my meter.

Who said anything about V4 and V5???

How can I help you if you won't work with me? I know there may be a communication gap and that's why I tried to be very specific in asking you to make certain checks. If you don't understand what I'm asking you to do, then please say so.

I still suspect the V1 circuit is faulty. I need you to work with me to prove or disprove this. Don't give me any more "value is correct" answers. I want numbers that you read on your meter.

[kwm488]

hi

i hope to report all pin voltage to you. so i test V4 and 5 also. but it kill my meter, do you mind to tell me why?

Did you touch your finger to the metal probe tip like I asked???
yes, volume 1 and 2 have hiss noise , but treble pot no reponse.

Now for V1... Look at the V1 tube Can you see the filaments glowing?
Yes


Now turn the amp off and make some resistance checks. First check each plate resistor for V1.
it is 100K



 Just put your ohm meter probes directly across each resistor. What are your measured values? Next, put one ohm meter lead on chassis ground. Connect the other lead DIRECTLY to V1 pin 3. What is your measured resistance? Repeat for pins 2 and 7.

sorry, the meter is dead

In summary, here are the measured numbers I want you to report...

Voltage on V3 pin 2.....
Voltage on V3 pin 7.....
Resistance across V1 pin 1 plate resistor.....100K
Resistance across V1 pin 6 plate resistor.....100K
Resistance between V1 pin 3 and chassis ground.....
Resistance between V1 pin 2 and chassis ground.....
Resistance between V1 pin 7 and chassis ground.....

[sluckey]

Resistance across V1 pin 1 plate resistor.....100K
Resistance across V1 pin 6 plate resistor.....100K

Did you actually measure those two 100K resistors with your meter before it died? Or are you reading a layout/schematic? Or are you reading the resistor with your eyes?

I can't say why your meter died. Even professionals occasionally kill test equipment.

[kwm488]

Yes. I test it before my meter die. It is 100k. And all of my resistor is new.

[kwm488]

Resistance between V1 pin 3 and chassis ground.....No response
Resistance between V1 pin 2 and chassis ground.....34k
Resistance between V1 pin 7 and chassis ground.....34k

[kwm488]

Hi

Do you mind to tell me. I follow your jtm45 layout to wire b+ wire from pt to gz34 pin 7 and pin 5. But I haven't add diode. I can't get any b+ that time. I find out I should wire to pin 4 and pin 6. Is this step hurt the gz34 tube ??? Because one just one b+ wire go to pin6 , but pin 4 no b+

Thank 

[sluckey]

Resistance between V1 pin 3 and chassis ground.....No response

And that's the problem with V1. You will get no guitar signal through the amp until that is fixed. Pin 3 and 8 should connect through a 820Ω resistor to chassis ground. Find out why that's no so. Refer to the attached pic...

Do you mind to tell me. I follow your jtm45 layout to wire b+ wire from pt to gz34 pin 7 and pin 5. But I haven't add diode. I can't get any b+ that time. I find out I should wire to pin 4 and pin 6. Is this step hurt the gz34 tube ??? Because one just one b+ wire go to pin6 , but pin 4 no b+

Whose layout? Ceriatone???
Those diodes are a good idea but they are not necessary. If you are not going to put diodes on the tube socket, then connect the PT HT leads directly to pin 4 and pin 6. You did not hurt the tube (if that's all you did).

[kwm488]

Hi
Thank you for help me debug.

I think that 330uf cap is not solder very good to turret. Will solder it again and measure. But I tried to do connection test before, it is connected. Anyways, will solder it again.

Yes, I follow ceriatone layout to build this amp. But I haven't add diode on gz34 tube socket. Sorry to ask again. I also email ceriatone for help, he think the b+ of 480vdc after gz34 is too high. Can I use 5u4gb to replace gz34 to test. Because I haven't gz34 anymore

Thank

[sluckey]

Fix one thing at a time. Forget the GZ34 for now. 480V ain't gonna hurt it or the EL34s.

[Jennings]

I won't start adding other suggestions to the melting pot here, as I think there's already enough to go on...just a comment to say RELAX...slow down, take one thing at a time and have patience.  If you panic or try to rush it all you'll probably just add further issues into the mix.  I know this from having done it myself!   

[kwm488]

hi sluckey

i find out the problem.  yes,  the 330uf and 820ohm resistor which connect to V1 pin 3 is not good (but it is sound when use meter to check connection, why). why it is no input and the V1 plate voltage is raise if 820 ohm and 330uf cap can't connect to pin3? i am interested, i hope to know more.

and i think i need to improve my soldering technique . this is my mistake, if all solder is good, i will have this problem. i learn a lot , i need to make sure every solder is good in the further. and i also resolder all turret already.

now, the plate voltage of V1 is 220v. B+ is 453 and my amp can sound now.

 
Thank you for your help. you help me very very lot. i can't sleep these day. today, i think can sleep very well.

[SleepLess]

Good that you found the issue! I agree with a prior statement though: your wiring is sloppy, you need to shorten your wires! It will give a clearer view of the amp and reduce hum as well. A good, short wiring is essential in these amps if you want to enjoy 100% of their abilities...

[kwm488]

Thank everyone help me.

I will cut the unuse wire in the further amp project. But this jtm45 used mercury rs transformer. It have many opintion, can choose el34, 6l6, kt66. So I keep the wire long enough if I want to use other tube in the future.

[Ed_Chambley]

The additional length of wire needed to rewire tube sockets to accept different power tubes is very minimal.  Simply strip all power tube wires just a little further than the longest run you have.  This will allow you to reposition the wiring in any way you want to.  I think they guys were not saying to stretch the wiring and make them have no slack whatsoever.  They were just telling you to get rid of most of the excess wire.

Also, Mercury makes great transformers, but I cannot tell any difference in Power Transformers between Hybour, Hammond.  I am not sure where Doug sources his Transformers, but I have bought a few from him and they work very well.  Output transformers are a little different.  I replaced a Hybour in a JTM 45 build with a Mercury and it did make a very noticeable difference.  Mainly in the clarity when playing a Telecaster