Hi,
I have a potted power transformer with 450-0-450@230mA and 580-0-580@175mA secondaries.
I want to use it for a guitar amplifier and havent built a powerful valve amp before.
Any suggestions on what tube configuration in the output stage would lap up these transformer specifications?
I know its good for 150W continuous which is nice
, i dont have an output transformer yet so i have a blank canvas!
Very interested to hear some opinions of what will be a good match! maybe i could find an excuse to incorporate my MV rectifiers (naaa thats silly).
I have a potted power transformer with 450-0-450@230mA and 580-0-580@175mA secondaries.
I want to use it for a guitar amplifier and havent built a powerful valve amp before.
Any suggestions on what tube configuration in the output stage would lap up these transformer specifications?
I know its good for 150W continuous which is nice
, i dont have an output transformer yet so i have a blank canvas!Very interested to hear some opinions of what will be a good match! maybe i could find an excuse to incorporate my MV rectifiers (naaa thats silly).
If you are building a guitar amp that will ever be sold you must think about the eventual retubing that will happen. The average guitar player will take the amp to a guitar amp tech or a music store. The selection of available tubes from these two sources is very small. For the voltage levels you speak of there is the EL34, the KT88, and the 6550.
If you are building the amp for your own use you can use whatever you want. The quick thought would be a pair of 813's but the filaments get rather fragile after a lot of use. The more conventional design would be to use sweep tubes (TV line output). I built a few guitar amplifiers that used a pair of 6LW6 sweep tubes to make 150 watts from a 700 volt supply about 10 years ago.
OPT ? I used some old military surplus power transformers. The 2200 VCT secondary became the primary, and the 115 volt primary became the secondary. Not exactly HiFi but it made for an extremely loud guitar amp. At least one of these is still alive and working. I retubed it for the first time about a year ago.
If you are building the amp for your own use you can use whatever you want. The quick thought would be a pair of 813's but the filaments get rather fragile after a lot of use. The more conventional design would be to use sweep tubes (TV line output). I built a few guitar amplifiers that used a pair of 6LW6 sweep tubes to make 150 watts from a 700 volt supply about 10 years ago.
OPT ? I used some old military surplus power transformers. The 2200 VCT secondary became the primary, and the 115 volt primary became the secondary. Not exactly HiFi but it made for an extremely loud guitar amp. At least one of these is still alive and working. I retubed it for the first time about a year ago.
Tubelab - I love your style!
As for the transformer - if you haven't built a big tube amp - please be careful. You are talking about 1160VAC (or 900 if you use the inner taps) either of which can kill you easy enough. Please do your homework.
Aside from that it should be good to go. I second the using standard tubes - ones in current production - in 20 years a large number of NOS tubes available now - will be gone.
As was said, a quad of el34, 6550 or KT88 will give you lots of power - and meet the easy to find and replace need.
As for the transformer - if you haven't built a big tube amp - please be careful. You are talking about 1160VAC (or 900 if you use the inner taps) either of which can kill you easy enough. Please do your homework.
Aside from that it should be good to go. I second the using standard tubes - ones in current production - in 20 years a large number of NOS tubes available now - will be gone.
As was said, a quad of el34, 6550 or KT88 will give you lots of power - and meet the easy to find and replace need.
This amp will be for personal use , i am intrigued by this 6LW6 tube, i cant find any data on google about these tubes?!
I can squeeze the output transfomer down to 738VDC from my 580-0-580@175mA tap (it has -10% taps), which is ballpark for 150W from these tubes.. Hmmm.
If they are cheaper than EL34/6550's then this is quite attractive.
As for OPT, i would try and go surplus too, buying new ones is too much for me.. but this is only in the idea stage at the moment so i havent given OPT much thought. Can you get the frequency response needed for a guitar from a power fransformer in reverse?
, i am intrigued by this 6LW6 tube, i cant find any data on google about these tubes?!I can squeeze the output transfomer down to 738VDC from my 580-0-580@175mA tap (it has -10% taps), which is ballpark for 150W from these tubes.. Hmmm.
If they are cheaper than EL34/6550's then this is quite attractive.
As for OPT, i would try and go surplus too, buying new ones is too much for me.. but this is only in the idea stage at the moment so i havent given OPT much thought. Can you get the frequency response needed for a guitar from a power fransformer in reverse?
The 6LW6 was from the end of the vacuum tube TV era. They are the biggest sweep tubes that I have run across. Several varieties were produced, and some have huge heat radiating fins welded to the plates. These can dissipate 60 to 80 watts without showing color. The 6LW6 is getting hard to find in the US and probably even harder to find elsewhere. 10 years ago they could be bought on Ebay for $5 each. I bought all I could get. Now they fetch $10 (rarely) to $30 each.
See this thread for data and alternatives:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=106289&highlight=
Search the tube forums for 6LW6 to find other interesting info.
Hi,
Have obtained four 807 tubes and have sketched out a brief circuit topology for this guitar amp.
2x anode follower gain stages, one LTP splitter driving MOSFET source followers driving 2x 807 tubes in AB2 push pull. Im aiming to put the HT at 500v for about 75W.
Tubelab, you mentioned using power transformers as output transformers, i think i can get some huge filament transformers at LEAST 15A 6.3V. Can these be used with speaker connected accross the heater taps provided they can be wired for 115V to 240V primary?
How does it sound using a PT for an OPT in a guitar amp?
Have obtained four 807 tubes and have sketched out a brief circuit topology for this guitar amp.
2x anode follower gain stages, one LTP splitter driving MOSFET source followers driving 2x 807 tubes in AB2 push pull. Im aiming to put the HT at 500v for about 75W.
Tubelab, you mentioned using power transformers as output transformers, i think i can get some huge filament transformers at LEAST 15A 6.3V. Can these be used with speaker connected accross the heater taps provided they can be wired for 115V to 240V primary?
How does it sound using a PT for an OPT in a guitar amp?
Just an FYI, but have you seen the STC 807 datasheet? It's 5.5M and has a 75W AB2 design near the end.
http://www.retrovox.com.au/STC807.pdf
http://www.retrovox.com.au/STC807.pdf
Cheers Brett, i have looked at this schematic before.
Its why i decided to go 75 watt at 500V, thought it must be a fairly reliable scheme if the data sheet illustrates a design with it.
Im definatly going to use it as reference but im working on designing one at moment from first principals (a good way to better understand tubes in detail for me).
Any advice on using a power transformer as an output transformer? im looking to skimp on this area unless this thing works very well, then ill fork out £60 for a hammond or somthing a bit better.
Its why i decided to go 75 watt at 500V, thought it must be a fairly reliable scheme if the data sheet illustrates a design with it.
Im definatly going to use it as reference but im working on designing one at moment from first principals (a good way to better understand tubes in detail for me).
Any advice on using a power transformer as an output transformer? im looking to skimp on this area unless this thing works very well, then ill fork out £60 for a hammond or somthing a bit better.
An old EI power transformer will not have enough bandwidth for HiFi, but they may do OK for a guitar or bass amp. I built at least a dozen amplifiers in my early teenage years using transformers and other parts salvaged from old TV sets. I most certainly did not have the ability to measure frequency response back then, and probably didn't understand the concept (it was a long time ago). Volume was king and my amps absolutely screamed.
I never got a filament transformer to work too well for an OPT since they are made to operate with 240 VAC or less on the primary. The plate to plate voltage in a 75 watt P-P amp can approach 800 volts. I used the HV center tapped secondary as the primary, and tied all of the filament windings in series for the secondary. Leave the original primary unconnected. Look for a power transformer with 3 filament windings of 3 amps or more. If your transformer has only 2 windings (6.3 and 5 V) use a 4 ohm or 2 ohm speaker cabinet.
My top secret (not any more) trick with toroids is to start with an isolation transformer that has 4 120 volt windings. Wire them all in series. Use this as the primary, and wind a new secondary on top of the existing windings. Experiment with the different combinations of series connections to get the best HF response. Really big toroids (500+ VA) don't seem to work well. Expect to run them at about 1/4 of their VA capability if you want good LF response.
Top secret number two. A common surplus find is a creature called an industrial control transformer. They come in several flavors. The ones with a 480 volt center tapped primary (2 240 volt windings) and a 24 volt secondary make a good bass guitar OPT (3200 ohm CT primary, 8 ohm secondary or 1600 / 4). Some are lossier than others, the HF response is lousy, but most will go to 5 or 10 KHz. Your speakers won't. A rarer find is 600 volt to 24 volt. these work out to 5K / 8 ohms. Again run them at about 1/4 to 1/8 of their rated capacity, and avoid the really big ones. The ones with welded laminations are lossier than stacked lams.
Old HV transformers from ham radio transmitters work too. A transformer with a 115 volt primary and a 2300 VCT secondary will work as an OPT. Again some work better than others. Just try what you can find.
I experimented with parts salvaged from old TV sets. Junk B/W (color was only for rich people) were tossed in the trash. I brought home a fresh chassis every week or so, kept the tubes, transformers, caps, resistors, and tube sockets, tossed the rest back into the trash. I wired stuff up, and sometimes it worked, most of the time it didn't, sometimes it blew up. I didn't care, parts were free, and I learned a lot by tinkering.
When I got to High School, I enrolled in a three year (vacuum tube) electronics program (sadly no longer offered). I told the teacher about some of my amplifiers, and he told me that "you can't do that, it won't work." I walked into class one day with my guitar and amplifier, and proceeded to blast everyone clean out of the room. One of the resident metal heads really liked it, he wound up buying it from me. Been building stuff my own way ever since!
I never got a filament transformer to work too well for an OPT since they are made to operate with 240 VAC or less on the primary. The plate to plate voltage in a 75 watt P-P amp can approach 800 volts. I used the HV center tapped secondary as the primary, and tied all of the filament windings in series for the secondary. Leave the original primary unconnected. Look for a power transformer with 3 filament windings of 3 amps or more. If your transformer has only 2 windings (6.3 and 5 V) use a 4 ohm or 2 ohm speaker cabinet.
My top secret (not any more) trick with toroids is to start with an isolation transformer that has 4 120 volt windings. Wire them all in series. Use this as the primary, and wind a new secondary on top of the existing windings. Experiment with the different combinations of series connections to get the best HF response. Really big toroids (500+ VA) don't seem to work well. Expect to run them at about 1/4 of their VA capability if you want good LF response.
Top secret number two. A common surplus find is a creature called an industrial control transformer. They come in several flavors. The ones with a 480 volt center tapped primary (2 240 volt windings) and a 24 volt secondary make a good bass guitar OPT (3200 ohm CT primary, 8 ohm secondary or 1600 / 4). Some are lossier than others, the HF response is lousy, but most will go to 5 or 10 KHz. Your speakers won't. A rarer find is 600 volt to 24 volt. these work out to 5K / 8 ohms. Again run them at about 1/4 to 1/8 of their rated capacity, and avoid the really big ones. The ones with welded laminations are lossier than stacked lams.
Old HV transformers from ham radio transmitters work too. A transformer with a 115 volt primary and a 2300 VCT secondary will work as an OPT. Again some work better than others. Just try what you can find.
I experimented with parts salvaged from old TV sets. Junk B/W (color was only for rich people) were tossed in the trash. I brought home a fresh chassis every week or so, kept the tubes, transformers, caps, resistors, and tube sockets, tossed the rest back into the trash. I wired stuff up, and sometimes it worked, most of the time it didn't, sometimes it blew up. I didn't care, parts were free, and I learned a lot by tinkering.
When I got to High School, I enrolled in a three year (vacuum tube) electronics program (sadly no longer offered). I told the teacher about some of my amplifiers, and he told me that "you can't do that, it won't work." I walked into class one day with my guitar and amplifier, and proceeded to blast everyone clean out of the room. One of the resident metal heads really liked it, he wound up buying it from me. Been building stuff my own way ever since!
Wow cheers for that valuable info! you only get knowledge like that from time and experience..
Think ill end up using a PT then, if theyre good for 5-10Khz thats just about acceptable for a guitar amp id guess and most importantly cheap!
If using the secondary of an HV EI core as the primary of the OPT is it a requirement to match the RMS current of the output tubes at full power to the secondaries current rating for proper operation?
Think ill end up using a PT then, if theyre good for 5-10Khz thats just about acceptable for a guitar amp id guess and most importantly cheap!
If using the secondary of an HV EI core as the primary of the OPT is it a requirement to match the RMS current of the output tubes at full power to the secondaries current rating for proper operation?
tubelab.com said:
Oh my! Thank you thank you! I have several of these in NOS condition! They look really nice and size wise (they look beefy) look like they should handle 20watts - they are in the 70-200VA range --- and 20watts into a guitar speaker can be quite loud! Thank you! Definitely going to try this out... -Sean
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