Safety wise, I am more concerned about the new main filter capacitors that have been secured to the chassis with hot glue and have the terminals facing the bottom; the old leaky ones have been left connected in the circuit by the way. They are right next to the new mains switch with exposed solder lugs.
IMHO
Sale the stock amp, and buy the correct parts to build a new EL34 amp. There are several experienced members here who shall be Happy to guide you during the entire exercise of building the new amp.
Regards,
Anwesh
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i understand what your saying, the one amp i had modded that used to use 6v6's and now uses EL34's/6CA7's ive been playing it for over a year now with no problems and it has quite abit more power then the one that is still running 6v6's, i only have to turn the modded el34 amp up to 2 vol and the amp with the 6v6's i have to turn it up 8 or so to match the vol of the el34 amp but i can hear that im maxing it out that why i started this whole blog is to just mod the 6v6 amp to match the other amp witch is running el34's. By the way, I'm also an R/C airplane and EDF Jet guy and EDF stands for electric ducked fan and i have added a 2nd edf to some of my jets using only the one 4cell 14.8v 2200mAh with a C rating of 50 thats how fast the batt will dicharge and it didn't start a fire and i did get 2X the power so im corn fuzed with all your blathering about horsepower and whatever stuff i already know butt thank you anyways for your insight
I think I was clear enough.
Either you do it empirically and it's risky.
either you do it in a technical way and you have chances that it works in the long term but it is MUCH more work.
Power transformer looks to be big enough to support EL34/6L6, unless it has been weakened by past overheating. The volume imbalance between the EL34 and 6V6 is due to gain difference, not power. Maybe the 6V6 tubes on your amplifier have become weak; they are usually run at maximum ratings on this kind of amplifiers, while the EL34 will work at reduced rate and will last forever. Have you tried to replace the 6V6 with EL84? This will only require an adapter and maybe the replacement of the cathode resistor, as I wrote in the previous post. EL84 will not overload the transformers and it sounds good.
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thanks for being cool and just giving me nothing but best idea, the dictograph amp that was modded to use EL34's i have been playing loud chunky guitar with it for over a year now and it still sounds killer never blew a fuse the only thing that i did was after over a year i replaced the 6CA7's with EL34's and I just did that a week ago, I've play it every day up full for 2 or 3 hours at a time no problems yet fingers crossed still sound killer and i do get way more watts from the EL34's then the 6V6's and if over a year give or take the tubes start leak that worth it 50 60 bucks for a match set of tubes no big deal thats like changing spark plugs
So already, you have to start by relaxing.
Then no, I'm not a guitarist, but I've been repairing amps for nearly 30 years and when I say amps, it's several hundred.
I say that I am a transistor man because I started at the time of ... transistors and that, when I started, the lamps were outdated, so I considered that ... it was outdated, until 5 or 6 years ago when a customer insisted that I try to repair his AirTight ATM1s, which I did, and literally dove into the lamp (thanks to many of people here). Since then I have progressed a lot but I am still what I consider to be a "child" because it takes a lot of time and learning work to one day be really comfortable with lamp technology.
This is why, not knowing you and, answering your initial question, I warned you.
Now I think you are an adult, you know there is a risk of fire if you don't do things right and I had to warn you as made other people here.
With that, have a nice day.
Then no, I'm not a guitarist, but I've been repairing amps for nearly 30 years and when I say amps, it's several hundred.
I say that I am a transistor man because I started at the time of ... transistors and that, when I started, the lamps were outdated, so I considered that ... it was outdated, until 5 or 6 years ago when a customer insisted that I try to repair his AirTight ATM1s, which I did, and literally dove into the lamp (thanks to many of people here). Since then I have progressed a lot but I am still what I consider to be a "child" because it takes a lot of time and learning work to one day be really comfortable with lamp technology.
This is why, not knowing you and, answering your initial question, I warned you.
Now I think you are an adult, you know there is a risk of fire if you don't do things right and I had to warn you as made other people here.
With that, have a nice day.
Mono amplifiers from the '50 are fun to work with. Repurposing them as instrument amplifiers gives more room to experimentation and sometimes the outcome is better than restoring them for Hi-Fi use. Maybe you should have posted your request on that section of the forum.
Your amplifiers have been recovered from good quality record players, I attach the original advertising from 1956. If you have some time to spare, I suggest to rebuild the power supply section: add a tag board to hold the capacitors, like any classic tube guitar amplifier. The way they are installed now is unfriendly to service, and does not look professional. They can detach during transport and short-circuit the tube rectifier.
Your amplifiers have been recovered from good quality record players, I attach the original advertising from 1956. If you have some time to spare, I suggest to rebuild the power supply section: add a tag board to hold the capacitors, like any classic tube guitar amplifier. The way they are installed now is unfriendly to service, and does not look professional. They can detach during transport and short-circuit the tube rectifier.
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The tube rectifier often drops 50V from the B+.
Then converts to:
The solid state rectifier often drops 1V from the B+.
You will most likely need a series resistor to drop about 49V, give or take.
Make that change without accounting for the now-needed series resistor, and expect more B+ voltage, more B+ load current, and more heating of the power transformer, output transformer, and output tubes.
All modifications might be safe, but properly designed modifications are more safe than others.
Just my opinion.
Then converts to:
The solid state rectifier often drops 1V from the B+.
You will most likely need a series resistor to drop about 49V, give or take.
Make that change without accounting for the now-needed series resistor, and expect more B+ voltage, more B+ load current, and more heating of the power transformer, output transformer, and output tubes.
All modifications might be safe, but properly designed modifications are more safe than others.
Just my opinion.
You basically have a chassis
with needed transformers
and enough sockets to wire up a push pull amplifier.
with a guitar type preamp and tube rec
The modified amplifier is " louder"
Because the original mods done changed the whole preamp
section to a guitar style preamp with instrument level gain.
He doesn't need to change the transformer
because it is a healthy sized transformer.
and it is still wound to a ratio which works for
6V6 or 6L6 / 6CA7
Anyone should have caught by the labeled
output taps that the impedance has been labeled
according to the tubes used.
6V6 would use around 8k to 10k primary
6L6/6CA7 use around 4k to 5k primary
so bingo bango the transformer is the right ratio.
As you see the 6V6 taps are 16 , 8, 4 ohm
With 6L6 or 6CA7
the 16 ohm tap becomes 8 ohms
the 8 ohm tap becomes 4 ohms
Same ratio.
8 to 10k primary = 6V6
4 to 5k primary = 6L6/6CA7
with needed transformers
and enough sockets to wire up a push pull amplifier.
with a guitar type preamp and tube rec
The modified amplifier is " louder"
Because the original mods done changed the whole preamp
section to a guitar style preamp with instrument level gain.
He doesn't need to change the transformer
because it is a healthy sized transformer.
and it is still wound to a ratio which works for
6V6 or 6L6 / 6CA7
Anyone should have caught by the labeled
output taps that the impedance has been labeled
according to the tubes used.
6V6 would use around 8k to 10k primary
6L6/6CA7 use around 4k to 5k primary
so bingo bango the transformer is the right ratio.
As you see the 6V6 taps are 16 , 8, 4 ohm
With 6L6 or 6CA7
the 16 ohm tap becomes 8 ohms
the 8 ohm tap becomes 4 ohms
Same ratio.
8 to 10k primary = 6V6
4 to 5k primary = 6L6/6CA7
The builder labeled the chassis with 5U4
likely original rectifier.
So 3 amps
Really all we know from the schematics on the chassis
Center tapped high voltage.
5 volt tap around 3 amps
6 volt tap
no center tap on 6 volt winding
so he added virtual ground/ hum balance pot.
no need to bypass tube rectifier.
the transformer looks very large because
it has 3amp 5 volt tap for tube rectifier.
might as well use it.
otherwise if bought.
much more expensive transformer.
dont know if it has negative bias tap on transformer.
for fixed bias
so could be cathode bias.
just realized original rectifier is 5Y3 heater= 2 amps
5U4 pulls 3amps
GZ34 much more common guitar amp rectifier.
only needs 1.9 amps for heater, less voltage drop.
might be different pinout.
but better rectifier for current draw on 5 volt winding.
6 volt winding, for 12ax7, 12at7, 12au7, 6C4 and 2x 6V6
would be around 2 amps.
EL34, 6CA7 = 1.5 amps each
removing one 12at7 frees up .3 amps
why he used the 6C4...I dont know.
Im guessing amp is around 15 to 18 watts
just change the preamp.
Beam Tetrode better tube
more efficient , less heater current.
6V6 better
5U4 pulls 3amps
GZ34 much more common guitar amp rectifier.
only needs 1.9 amps for heater, less voltage drop.
might be different pinout.
but better rectifier for current draw on 5 volt winding.
6 volt winding, for 12ax7, 12at7, 12au7, 6C4 and 2x 6V6
would be around 2 amps.
EL34, 6CA7 = 1.5 amps each
removing one 12at7 frees up .3 amps
why he used the 6C4...I dont know.
Im guessing amp is around 15 to 18 watts
just change the preamp.
Beam Tetrode better tube
more efficient , less heater current.
6V6 better
First of all, I'm always relaxed, I don't know maybe its cuz of all the gigs i've played over the passed 40 years and all the times i've been ZAPPED!!! and talked to god for a moment waiting for my eye sight to come back! cuz any player thats been giging cuz they love playing live and love music has been ZAPPED!!! more then 10 times I've takin some big Volts EZ 50 times or more my whole life, from water pipes, bad ground at bar ,my favrit, wrong polarity on the amp then going up to sing in the mic ZAPP! thats good one, i don't know where your from but when you say (lamp) are you talking about your desk lamp, dah! i know what you mean, sure tubes light up a little but its not a flash light its a tube for a tube amp not a lamp, from what you said in your last text you shouldn't be saying anything about tube amps to anybody!! thanks for warning me that i might get ZAPPED! you should read what (Whitedragon) tolled me and how it was said, now that person knows what there talking about! strait to the point! Thank you Whitedragon as for you, you said it yourself your a child, and I say,,, that needs to grow up giving advice about (lamps amps) Tube amps! have yourself a very nice day,week,month,year oh yah Life! im sorry dude! im sure your a real cool guy you were only trying to help thank you very much!!!!
??? other poster said child not me.
you already have modded amp.
So just trace circuits, and draw schematic
then build/drill chassis like previous builder.
as mentioned you already have chassis and transformers and sockets.
from basic detective work.
you have 2 amp 5 volt tap
2 amp 6 volt tap.
if you want to exceed both those taps by 1 amp
or pull a extra current. Its up to you.
modded amp louder, cause it has enough preamp gain.
Builder changed preamp.
5U4 direct heated
uses 3 amp not 2amp
make transformer hot.
pentode 1.5 amp heater
beam tetrode .5 amp heater
pentode make transformer hot
loose power. not more power
6C4 drop on floor, not miss
or sell to Magnavox / Ampeg guy
chassis has 12ax7, 12at7, 12au7
make better pre with 2x 12ax7 and 12au7 phase split.
already have sockets.
you want cobbler amp make cobbler amp.
people try to teach.
280 volt is 12 to 18 watt
6CA7 need 380 volt for 30 watt
450 volt for 50 watt
load line is poop on 280 volt
you already have modded amp.
So just trace circuits, and draw schematic
then build/drill chassis like previous builder.
as mentioned you already have chassis and transformers and sockets.
from basic detective work.
you have 2 amp 5 volt tap
2 amp 6 volt tap.
if you want to exceed both those taps by 1 amp
or pull a extra current. Its up to you.
modded amp louder, cause it has enough preamp gain.
Builder changed preamp.
5U4 direct heated
uses 3 amp not 2amp
make transformer hot.
pentode 1.5 amp heater
beam tetrode .5 amp heater
pentode make transformer hot
loose power. not more power
6C4 drop on floor, not miss
or sell to Magnavox / Ampeg guy
chassis has 12ax7, 12at7, 12au7
make better pre with 2x 12ax7 and 12au7 phase split.
already have sockets.
you want cobbler amp make cobbler amp.
people try to teach.
280 volt is 12 to 18 watt
6CA7 need 380 volt for 30 watt
450 volt for 50 watt
load line is poop on 280 volt
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The simplest way to avoid transformer overload with something like this is to off-load all of the heaters to a separate 6.3 volt transformer. 50-72 VA is plenty and is only $20-30. Your increased B+ with the SS rectifier is less of an issue then because drawing a bit more off the B+ is ok if the total load is the same or less.
If the 6v6’s are just swapped out for higher current tubes (even if the Iq is adjusted with the cathode resistor) they still might not last any longer because the screen voltage will be way too high. When you clip, the screen current will be excessive because all of that extra cathode emission has to go somewhere. When the plate current is too low at the knee it goes to the screen. If Vg2 is adjusted down to properly match the load line this doesn‘t happen. THEN you will get the increase in lifetime. A side benefit is an increase in gain and lower crossover distortion, because the proper Iq is achieved at a less negative Vg1 compared with the case of excessive Vg2. People tend to forget about that extremely useful knob they can turn when tweaking - just tying it to the B+ is great for a stock 6v6 or EL84 on 250-280V where you’re maxing it, but not when trying to run a bigger tube below ratings.
If the 6v6’s are just swapped out for higher current tubes (even if the Iq is adjusted with the cathode resistor) they still might not last any longer because the screen voltage will be way too high. When you clip, the screen current will be excessive because all of that extra cathode emission has to go somewhere. When the plate current is too low at the knee it goes to the screen. If Vg2 is adjusted down to properly match the load line this doesn‘t happen. THEN you will get the increase in lifetime. A side benefit is an increase in gain and lower crossover distortion, because the proper Iq is achieved at a less negative Vg1 compared with the case of excessive Vg2. People tend to forget about that extremely useful knob they can turn when tweaking - just tying it to the B+ is great for a stock 6v6 or EL84 on 250-280V where you’re maxing it, but not when trying to run a bigger tube below ratings.