OK. Its not the FREDS.
I wired the amp up and cliped the FREDS installed all the tubes and turned it on.
The fuse blew intsantly.
Now what?
Should clip the leads from the PT and try again?
If so. How should I do this? Clip every wire going to board from the PT?
What about the wires going to the choke?
Last night I cliped every lead from the board that was connected to the PT. And left the choke and PT connected and it still blew fuse. Am I supposed to clip those leads to?
Nick
I wired the amp up and cliped the FREDS installed all the tubes and turned it on.
The fuse blew intsantly.
Now what?
Should clip the leads from the PT and try again?
If so. How should I do this? Clip every wire going to board from the PT?
What about the wires going to the choke?
Last night I cliped every lead from the board that was connected to the PT. And left the choke and PT connected and it still blew fuse. Am I supposed to clip those leads to?
Nick
Look carefully at the leads to make sure no "hairs" are fraying out anywhere. Are they soldered to the PCB or did you use terminals. I You can start by disconnecting the red wires from the PT to the PCB. You can leave the choke.
So it blows with no tubes installed at all? Inspect carefully between the tube sockets and the PCB to make sure you don't have any stray solder or leads floating around under them.
Russ
So it blows with no tubes installed at all? Inspect carefully between the tube sockets and the PCB to make sure you don't have any stray solder or leads floating around under them.
Russ
So if it is my power tranny. At least I can get the one I wanted at the beginning of build
A Hammond 374BX
I ended up getting the Allied 6k7vg to save money. It had a very slight hum from the beginning that I was never too fond of.
I have a question though. Will the Hammond bolt in the same holes as the Allied? I have a lot of time invested in this chassis and I don't want to make any new holes.
Second do you guys think its the PT.
If so I'll go ahead and order one. I think its the PT personely. Thats what I thought from the beginning. It was Just a hunch.
But I don't want to pull the trigger on anything until I here from you guys...
Nick
A Hammond 374BX
I ended up getting the Allied 6k7vg to save money. It had a very slight hum from the beginning that I was never too fond of.
I have a question though. Will the Hammond bolt in the same holes as the Allied? I have a lot of time invested in this chassis and I don't want to make any new holes.
Second do you guys think its the PT.
If so I'll go ahead and order one. I think its the PT personely. Thats what I thought from the beginning. It was Just a hunch.
But I don't want to pull the trigger on anything until I here from you guys...
Nick
rknize said:
I'm not sure on the cathode resistors. Whatever that is on Georges part list is what I used.
I noticed the Transformer was pretty dang warm when the amp went out. I have never noticed it this warm before. So thats where the hunch of thinking maybe my PT went out came from.
Nick
This is the most logical conclusion, but there are a few other possibilities. A breakdown in the insulation of the power switch could cause this, but I have never seen it happen.
There was another builder that had a similar experience. It turns out that the sharp edge on the chassis cut through the insulation of one of the power transformer wires right where the wires went through the chassis, casuing a blown fuse. If this is the case it may be possible to put some sleeving on the offending wire and make sure that the metal edge is free from burrs. A rubber grommet of other non metallic sleeve should be used in the chassis hole where wires go through.
To confirm a bad transformer, I would make sure that all of the secondary wires are indeed not connected to anything, and taped up or otherwise prevented from touching each other of anything else. The only wires connected should be the two black ones. If the fuse still blows, disconnect the black wire from the power switch the fuse should not blow, but if it does the switch is bad. If the wires are not damaged then the transformer is likely bad.
It is very rare for a transformer to fail in this manner, but it is possible. Allied has been known to replace them for free if this happens.
Well the last thing to check is the switch. If the switch is good I'll pull the transformer and inspect the the wires. But I don't think its the wires. Either way. I am going to check eveythign like you said. If it still points to the PT I am going to get a Hammond 374BX,
Thanks for everybodys help again. You guys really come through when called upon..
Nick
Thanks for everybodys help again. You guys really come through when called upon..
Nick
The Allied 6K7VG is rated for 150 mA, but it is also rated for operation at 50Hz. When used at 60Hz it will handle 175 mA. It IS a Hammond in disguise so like all 200 series Hammonds it gets HOT. This seems to be normal for the breed. I have been using the Allied 6K7VG and 6K56VG for ever. I started making a lot of guitar amps with the 6K7VG about 15 years ago. I never paid much attention to the ratings, so I just kept making bigger and bigger amps. In all that time I have seen two fail, one was provoked by an "amp expert" with a 15 amp fuse, and my Lexan amp got waterlogged during a hurricane and I kept using it until it died.
It is true that Hammond quality has declined, and they have obviously changed the recipie, since the transformers that you get today put out more voltage than the ones that I still have around here that are about 5 years old. The get hotter too.
My Industrial amp has an Allied transformer, I have the bias cranked up to 100 mA per tube for a total of 220 Ma from the transformer. Yes it gets pretty dang warm, but it has been like that for 3 years.
I have not used a Hammond 374BX, so I don't know the exact size, but the Allied 6K7VG is actually about 1/4 inch deeper (more laminations) than the Hammond 274BX. I have them both here. The 274BX is rated for 175 mA, and the Allied is rated for 150 mA, but is bigger and costs less. This is why I prefer the Allied transformer.
So your saying its a fluke and it would be ok to stay with the Allied?
What about the small hum I was getting from it. Do you think it was bad from the get go?
I get nothing through the speakers. Dead quite. But I could hear the PT hum from my seat. A very slight hum. But a hum none the less.
Do you think this wouls still be there with another Allied Transformer.
I was kind of hoping the Hammond 300 series would cure the hum problem I was having.
What do you think?
If I can save $50 I'm all for it. I just don;t want to end up with another failure or hum.
Do you get any hum from your Allied Transformers?
Nick
What about the small hum I was getting from it. Do you think it was bad from the get go?
I get nothing through the speakers. Dead quite. But I could hear the PT hum from my seat. A very slight hum. But a hum none the less.
Do you think this wouls still be there with another Allied Transformer.
I was kind of hoping the Hammond 300 series would cure the hum problem I was having.
What do you think?
If I can save $50 I'm all for it. I just don;t want to end up with another failure or hum.
Do you get any hum from your Allied Transformers?
Nick
Transformers usually fry slowly and stink up the room when they go. It is rare for one to just die, but there is one more thing to check.
Disconnect the amp from power, and turn it off. Disconnect all transformer wires from the amp. Connect one lead of your multi meter to the chassis. Set the meter to OHMS. Touch the other lead to each of the transformer leads. ANY reading from any lead other than the thin grey one indicates a short in the transformer. If there is a low reading (under 1000 ohms) remove the transformer from the amp.
After removing the transformer from the amp repeat this test with one lead connected to the transformer case and the other touched to each transformer wire. If there is a low reading the transformer has developed a short. This is a potentially unsafe situation and the transformer must not be used. This type of failure is an indication of poor workmanship. and should be replaced by the manufacturer.
If there was a low reading when the transformer was in the amp, but it is no longer present after removal, then a wire is getting pinched or cut somewhere.
Disconnect the amp from power, and turn it off. Disconnect all transformer wires from the amp. Connect one lead of your multi meter to the chassis. Set the meter to OHMS. Touch the other lead to each of the transformer leads. ANY reading from any lead other than the thin grey one indicates a short in the transformer. If there is a low reading (under 1000 ohms) remove the transformer from the amp.
After removing the transformer from the amp repeat this test with one lead connected to the transformer case and the other touched to each transformer wire. If there is a low reading the transformer has developed a short. This is a potentially unsafe situation and the transformer must not be used. This type of failure is an indication of poor workmanship. and should be replaced by the manufacturer.
If there was a low reading when the transformer was in the amp, but it is no longer present after removal, then a wire is getting pinched or cut somewhere.
I don't hear anything, but my hearing isn't that good and the ambient noise is usually rather high from the air conditioning, street noise, 747's flying overhead (we are in the approach path for FLL) etc. The Allieds that I have in my amps are all about 5 years old too. I bought a bunch right before the price increase when they were dumb enough to offer free shipping on orders over $100. The newer ones may be worse.
It is a common complaint for low level hum from Hammond 200 series transformers. I have not heard much from the users of the Allied transformers. They have more metal in the core which reduces the idle current and should reduce the buzz. The 300 series has the extra laminations which are needed for 50Hz operation, thus reducing the buzz. People say that they are built better, but I have never used one since I am cheap, and I still have a few of the old Allieds left.
Too late. I already pulled the PT.
I checked the power switch. It was good. I pulled the tranny and inspected the wires. they were good. I have a pretty big hole cut for them to go through..
I then tested the PT for a short. I didn't find any...
I guess it just went bad???
Oh well. It happenes I guees. Why not me.
Now I have to decide which to get the. The Allied I had or the 300 series Hammond.
I
Nick
I checked the power switch. It was good. I pulled the tranny and inspected the wires. they were good. I have a pretty big hole cut for them to go through..
I then tested the PT for a short. I didn't find any...
I guess it just went bad???
Oh well. It happenes I guees. Why not me.
Now I have to decide which to get the. The Allied I had or the 300 series Hammond.
I
Nick
nikolas812 said:
Somebody correct me if I'm wrong, but if there is no short in the power transformer, then it isn't bad. Blindly replacing it won't fix the underlying problem and will only net you a spare power transformer.
Can you measure the DC resistance for each winding, and post the results here? Measure black to black, red to red, yellow to yellow, green to green, etc. Also measure black to red, black to yellow, black to green, so on and so forth.
Convince yourself that the transformer is bad before springing for another one.
Did the transformer get overheated from incorrect wiring, etc during the build? This usually results in loud buzzing followed by stinky smoke, although if caught early, the transformer could still function, especially if you never got to the smoke phase.
If it's bad either one winding is shorted to another, or to the transformer case, or a winding has failed open circuit. The windings should have very high resistance (megohms or "off-the-scale") on your meter between each other and between each winding and the case (ground), and should have very low resistance from one end to the other of each individual winding.
I suppose an open circuit won't pop a fuse, so focus on the short circuit possibilities.
Did the transformer get overheated from incorrect wiring, etc during the build? This usually results in loud buzzing followed by stinky smoke, although if caught early, the transformer could still function, especially if you never got to the smoke phase.
If it's bad either one winding is shorted to another, or to the transformer case, or a winding has failed open circuit. The windings should have very high resistance (megohms or "off-the-scale") on your meter between each other and between each winding and the case (ground), and should have very low resistance from one end to the other of each individual winding.
I suppose an open circuit won't pop a fuse, so focus on the short circuit possibilities.
If the transformer is indeed bad and you are not able to exchange it for a new one at Allied, you might consider upgrading to a better transformer with a bit more capacity on the B+ winding. I'm using the Edcor XPWR035, which barely gets warm in my Simple SE. Here are the specs:
370-0-370 @ 200mA
6.3 VCT @ 5A
5V @ 2A
Cost was $66. Only a bit more than the 6K7VG, but well worth it. Only downside is the 2-3 week wait Edcor seem to be running with these days.
All that said, the 6K7VG should have survived if you were using the 560-ohm cathode resistors that I believe are the default in the instructions. However if the transformer ran hot like a typical Hammond seems to these days and you were getting more like 500V B+, then you would technically be drawing more current with KT88s than the transformer is spec'ed at. This plus excessive heat from the hot-Hammond primary might have killed it (if it is indeed dead).
370-0-370 @ 200mA
6.3 VCT @ 5A
5V @ 2A
Cost was $66. Only a bit more than the 6K7VG, but well worth it. Only downside is the 2-3 week wait Edcor seem to be running with these days.
All that said, the 6K7VG should have survived if you were using the 560-ohm cathode resistors that I believe are the default in the instructions. However if the transformer ran hot like a typical Hammond seems to these days and you were getting more like 500V B+, then you would technically be drawing more current with KT88s than the transformer is spec'ed at. This plus excessive heat from the hot-Hammond primary might have killed it (if it is indeed dead).
I just got off the phone with Allied. I think there going to send me a new one. I'm waiting for them to call me back.
I don't know how to do resistence checks with my Volt meter. I have Fluke so I imagine its capable. But I 'm not too sure how to do it.
I do know how to check for shorts though. And I still can't find any. When grounded to the Case and checking all the wires. I don't get any shorts.
Black to black shorts
Yellow to yellow Shorts
Green to Green shorts
Red to Red does not Short. Should red to red short also.
Nick
I don't know how to do resistence checks with my Volt meter. I have Fluke so I imagine its capable. But I 'm not too sure how to do it.
I do know how to check for shorts though. And I still can't find any. When grounded to the Case and checking all the wires. I don't get any shorts.
Black to black shorts
Yellow to yellow Shorts
Green to Green shorts
Red to Red does not Short. Should red to red short also.
Nick
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