You must have exceeded its current rating or a short in your filament supply.
I don't think I exceeded the current rating, but I'm pretty close.
Transformer is rated for 6.3v @ 6A
I calculate 5.8A with the KT150's, which I actually haven't been running.. they sound pretty sterile at ~60% dissipation. I've been running the 6L6's so heater current is actually less. When I disconnect the lead from the transformer, I'm not reading any shorts in the heater wiring to ground.. not sure why the transformer crapped the bed.
One thing I DID learn.. I should have fused the heaters. That will be corrected when the new transformer comes in. I'll likely fuse the HT secondaries as well, transformers are expensive.. don't want to cook my iron.
I'm going to try and get the complete schematic drawn up and put on here today, it's entirely possible that I've made a terrible mistake somewhere.. though the amplifier was operating and sounding wonderful before this happened. Good thing I noticed that the pilot light was dim, which led me to investigate further.
Will update.
Transformer is rated for 6.3v @ 6A
I calculate 5.8A with the KT150's, which I actually haven't been running.. they sound pretty sterile at ~60% dissipation. I've been running the 6L6's so heater current is actually less. When I disconnect the lead from the transformer, I'm not reading any shorts in the heater wiring to ground.. not sure why the transformer crapped the bed.
One thing I DID learn.. I should have fused the heaters. That will be corrected when the new transformer comes in. I'll likely fuse the HT secondaries as well, transformers are expensive.. don't want to cook my iron.
I'm going to try and get the complete schematic drawn up and put on here today, it's entirely possible that I've made a terrible mistake somewhere.. though the amplifier was operating and sounding wonderful before this happened. Good thing I noticed that the pilot light was dim, which led me to investigate further.
Will update.
.. and I pulled the 6N1P out, because it does nothing but waste power. So total current with the KT150's would be more like 5.2A.
Schematic v1.4
Here's the amplifier schematic as it is right now.
Planning to add fuses on the filament secondaries and HT secondaries. Will also be adding a bleeder resistor to the PS section.
Use your imagination for the power switch. It's a Glassware rotary switch, allows for the filament transformers to be powered up for standby before the HT transformer is switched on. Didn't have the proper component in the schematic software I'm using (Jschem).
Here's the amplifier schematic as it is right now.
Planning to add fuses on the filament secondaries and HT secondaries. Will also be adding a bleeder resistor to the PS section.
Use your imagination for the power switch. It's a Glassware rotary switch, allows for the filament transformers to be powered up for standby before the HT transformer is switched on. Didn't have the proper component in the schematic software I'm using (Jschem).
canadatubedude: I wonder how warm your 6.3v transformer got? It being inside your chassis and close to it's max rating. I am running a Hammond 6.3 4A model 167 at 4A. It sits outside on top of my chassis and it gets fairly warm.
You could use the 6.3v 6 amp winding on the 378CX for a couple of the tubes and take some of the load off of your 167Q6. Kinda spread things out.
You could use the 6.3v 6 amp winding on the 378CX for a couple of the tubes and take some of the load off of your 167Q6. Kinda spread things out.
According to the tube data the kt150 uses just around 2A of filament current so with your SE stereo amp of 2 x kt150 you should be well within the current rating of your fil trans. There must have been something to take it over the edge. Was it a new trans? I just had a bad experience with a used 1.2A 6.3v fil trans. It worked good for about 10 minutes then it started to draw excess current. The amp is a new build so i was monitoring the bias current and noticed it started to runaway and i shut the amp down.
MelB: I hadn't really thought of how warm it got under the chassis.. probably pretty warm. Not much in the way of airflow, actually no air flow really.
I could use the filament supply from the 378CX, but then I'd be eliminating the standby.
If I powered up the PTX with it's 6.3volt source, and left the rectifier filament off.... how would that effect the rectifier with HV on the plates but no heater?
Or.. could I just eliminate the standby altogether? I kinda liked having it.. I'm under the impression that tubes should be well warmed before applying high voltage.
I could use the filament supply from the 378CX, but then I'd be eliminating the standby.
If I powered up the PTX with it's 6.3volt source, and left the rectifier filament off.... how would that effect the rectifier with HV on the plates but no heater?
Or.. could I just eliminate the standby altogether? I kinda liked having it.. I'm under the impression that tubes should be well warmed before applying high voltage.
the rectifier needs to be perfectly cold to start , never put a stand-by or pre-heater on that element!
In that case perhaps I'll just disconnect the blown hammond and rewire the switch to turn it all on at the same time, using the filament supply from the PTX.
Looks like I'll just have the entire circuit switch on at once, and replace the 5U4GB rectifier with a 5AR4. The 5AR4 should allow time for the other tubes to reach operating temperature.
The only thing I don't like about this is that the 5AR4 is a tiny little tube compared to my Sylvania 5U4GB... doesn't look at neat 🙁
The only thing I don't like about this is that the 5AR4 is a tiny little tube compared to my Sylvania 5U4GB... doesn't look at neat 🙁
The other tubes can have the full B+ without reaching temperature, it doesn't harm them in the circuit you built.
the 5ar4 is able to push as much current as your 5u4gb.
I don't know why you want to replace the 5u4gb ?, however it has 3 A filament requirements vs 2 amps for the 5ar4.
the 5ar4 is able to push as much current as your 5u4gb.
I don't know why you want to replace the 5u4gb ?, however it has 3 A filament requirements vs 2 amps for the 5ar4.
SS rectification
Hello from Greece! The tube rectification it is not good solution. You can use in your circuit SS rectification,no harm the tubes the voltage before heat,better sound,no waste of energy,no more tube problems (arc,slow power loss when the tube slowly dies,no unxpected tube failures).In SS rectification you can use more capacitance without problem!
Hello from Greece! The tube rectification it is not good solution. You can use in your circuit SS rectification,no harm the tubes the voltage before heat,better sound,no waste of energy,no more tube problems (arc,slow power loss when the tube slowly dies,no unxpected tube failures).In SS rectification you can use more capacitance without problem!
Canadatubedude do you have a link to buy that Mogami cable? Or did you just cut up a patch cord?
to say that it is not a good solution is rushing to conclusions.
Do you agree that in this application the power supply would benefit from dual 5ar4 ?, this would reduce 'sag' and keep a good tone.
@ MelB - I got the interconnect wire here..
https://www.tubedepot.com/products/mogami-w2330-interconnect-wire
Okay, been a busy day so far. I disconnected the separate Hammond 6.3v transformer, and hooked up the 6.3v CT from the power transformer. Moved by B+ source from the 5v CT to pin 8 on the rectifier socket, altered the power switch, and dropped in a 5AR4.
A lot less voltage drop.. 520v B+
The KT150's bias up right around 90% now, so that's good! The 6L6's and EL34's are well outside the safe zone at the moment, 6L6's red plated right away on "High"
I'm getting the following dissipations;
KT150 Low) 39w High) 53w
6L6GC Low) 33w High) 44w
EL34 Low) 32w High) 43w
https://www.tubedepot.com/products/mogami-w2330-interconnect-wire
Okay, been a busy day so far. I disconnected the separate Hammond 6.3v transformer, and hooked up the 6.3v CT from the power transformer. Moved by B+ source from the 5v CT to pin 8 on the rectifier socket, altered the power switch, and dropped in a 5AR4.
A lot less voltage drop.. 520v B+
The KT150's bias up right around 90% now, so that's good! The 6L6's and EL34's are well outside the safe zone at the moment, 6L6's red plated right away on "High"
I'm getting the following dissipations;
KT150 Low) 39w High) 53w
6L6GC Low) 33w High) 44w
EL34 Low) 32w High) 43w
..and the 5AR4 just nuked itself.
Turned it off, and then back on again about 5 seconds later.. lightshow, rectifier is toasted.
Surge voltage I'm thinking..
Turned it off, and then back on again about 5 seconds later.. lightshow, rectifier is toasted.
Surge voltage I'm thinking..
Thanks for the schematic, I'll take a look at that.
I will continue to post results.. positive or negative.
Amp is working again, pulled a 5U4GB out of an old television, and threw in some of the old EL34's I've retired from my guitar amplifiers. Just fired it up, sitting here looking at it. Going to let it run for awhile. Will likely pick up another indirectly heated rectifier, I'm thinking 5V4 or 5Z4, I can still get those in the coolio ST bottles.
I will continue to post results.. positive or negative.
Amp is working again, pulled a 5U4GB out of an old television, and threw in some of the old EL34's I've retired from my guitar amplifiers. Just fired it up, sitting here looking at it. Going to let it run for awhile. Will likely pick up another indirectly heated rectifier, I'm thinking 5V4 or 5Z4, I can still get those in the coolio ST bottles.
Yup. You must wait a few minutes after you shut those tubes off before turning back on. They stay warm for a bit and need come up slowly to gradually fill up your caps as they warm up.
Oh and thanks for the link.
Last edited:
Personally, I would feel inclined to use solid state FAST rectifiers instead. Much less hassle and you can always add a power resistor in series, if you really want some sag.
I sure hope you're not incinerating any Mullard EL34s in the course o of this project.
Sent from my LG-D801 using Tapatalk
I sure hope you're not incinerating any Mullard EL34s in the course o of this project.
Sent from my LG-D801 using Tapatalk
Last edited: