Hi again everyone,
Just wanting to see if any of you have any suggestions for a good SE EL84 amplifier to build, I am going to salvage output and power transformers and valves from my old heathkit S-33 and Rebuild it in a new chassis, But i have been thinkign mabey i shouldnt stick to the circuit they used and mabey i can build somethign different, possibly even with some diffrent driver tubes.
Many thanks,
OWen
Just wanting to see if any of you have any suggestions for a good SE EL84 amplifier to build, I am going to salvage output and power transformers and valves from my old heathkit S-33 and Rebuild it in a new chassis, But i have been thinkign mabey i shouldnt stick to the circuit they used and mabey i can build somethign different, possibly even with some diffrent driver tubes.
Many thanks,
OWen
mabey something like this?
I like the look of this because it is fairly simple, i could probably wire it all point to point useing just the component leads and keep it fairly small.
What sort of output power would this give out?
Would it work ok? any improvements that could be made? Or should i go for somethign completely different? if so any suggestions what i should go for?
Many thanks,
Owen
I like the look of this because it is fairly simple, i could probably wire it all point to point useing just the component leads and keep it fairly small.
What sort of output power would this give out?
Would it work ok? any improvements that could be made? Or should i go for somethign completely different? if so any suggestions what i should go for?
Many thanks,
Owen
Attachments
the output transformers i salvaged have three wires on primary side though, one too pin 7 and one too pin 9 and one too b+, not sure how i would go about wireing them up for that circuit? or would it simply be that i wire it up the same but instead of wireing the sacond wire to the el84 i put the resistor to that pin (pin 9 i think) and to B+ like ont the schematic.. and ignore the third wire ont he output tranny?
Looks good though, i might try it out and see what it sounds like, if i dont liek it it is no big deal i guess, there dont appear to be many differances between the different schematics i have found so cant be that hard to switch between them till i find one i like..
OWen
Looks good though, i might try it out and see what it sounds like, if i dont liek it it is no big deal i guess, there dont appear to be many differances between the different schematics i have found so cant be that hard to switch between them till i find one i like..
OWen
Hi Owen,
Here is another EL84 schematic called the "Minute" from SAC Thailand, the makers of SILK transformers.
I think the output transformer that they are using has a 5k impedance.
Good Luck
Norris
http://www.sacthailand.com/AmpMinuteEL84.html
Here is another EL84 schematic called the "Minute" from SAC Thailand, the makers of SILK transformers.
I think the output transformer that they are using has a 5k impedance.
Good Luck
Norris
http://www.sacthailand.com/AmpMinuteEL84.html
Norris Wilson:
That schematic looks pretty interesting, might give it a go first if i can find out about my output transformers.
Anyone:
How would i go abotu measureing my output transformers impedance? :S And what do i do about the fact they have three wires ont he primary side and most of the schematics only have two? :S
Many thanks,
Owen
That schematic looks pretty interesting, might give it a go first if i can find out about my output transformers.
Anyone:
How would i go abotu measureing my output transformers impedance? :S And what do i do about the fact they have three wires ont he primary side and most of the schematics only have two? :S
Many thanks,
Owen
The cct for the silk transformer amp is nothing too special, it is missing an earth connection at the junction of the two cathode resistors though.
As for measuring the impedance of the transformer, the easiest way to do it is to apply an ac voltage to the primary, and measure the voltage across the secondary.
Voltage ratio can then be determined, square that and you have the impedance ratio. So if the tranny is designed for an 8 ohm output, multiply the ratio by 8 and et voila, you have the primary impedance.
hope that this helps.
kind regards
bill
As for measuring the impedance of the transformer, the easiest way to do it is to apply an ac voltage to the primary, and measure the voltage across the secondary.
Voltage ratio can then be determined, square that and you have the impedance ratio. So if the tranny is designed for an 8 ohm output, multiply the ratio by 8 and et voila, you have the primary impedance.
hope that this helps.
kind regards
bill
Thanks for that bill! that was EXACTLY what i wanted.
I have noticed that the output section on all these amps is pretty much the same, only thing that really changes a lot is the Driver tubes. So mabey i will just experiment and come up with something i like the sound off.
Many Thanks,
OWen
I have noticed that the output section on all these amps is pretty much the same, only thing that really changes a lot is the Driver tubes. So mabey i will just experiment and come up with something i like the sound off.
Many Thanks,
OWen
Owen,
Your O/P trafos have ultralinear taps (shows how well I guess
). That opens up an interesting possibility. You can try Bandersnatch's exolinear topology. Instead of connecting the voltage amplifier's load resistor to B+, connect it to the O/P trafo's UL tap along with the EL84's screen grid. It's a slick form of NFB.
An ECC88 section probably has enough gain to achieve full power driving the EL84. It is enough for a triode wired EL84 without NFB. However, the 40+ mu 12AV7 family tubes I suggested do offer extra "breathing room" over the mu 33 ECC88. In North America, 5965s are INEXPENSIVE, but I can't say anything about UK cost.
Your O/P trafos have ultralinear taps (shows how well I guess
). That opens up an interesting possibility. You can try Bandersnatch's exolinear topology. Instead of connecting the voltage amplifier's load resistor to B+, connect it to the O/P trafo's UL tap along with the EL84's screen grid. It's a slick form of NFB.An ECC88 section probably has enough gain to achieve full power driving the EL84. It is enough for a triode wired EL84 without NFB. However, the 40+ mu 12AV7 family tubes I suggested do offer extra "breathing room" over the mu 33 ECC88. In North America, 5965s are INEXPENSIVE, but I can't say anything about UK cost.
i just read that the 12AV7 is pin compattable with the 12AX7 and 12AU7 so would it be possible to build the amp useing one of these (As i have ECC81, 82 and 83 lying around) and then just swap it out like a straight swap with the 12AV7 when i manage to get some (if i can find them)? thinkign it might be a good tube to upgrade one of the channels in my PA amp aswell (useing it for guitar and bass) as it has higher gain than the 12AU7's they are useing in the input channels as standard?
Many Thanks,
Owen
Many Thanks,
Owen
found some on ebay, they seem cheap enough here aswell, matched pair of JAN GE 5965s come in at £6.50 inc p&p there are also GE black plate version but they are £6 each and normal GE version which is about £5 each.. so the JAN ones seem best.. might order a couple of matched pairs and see, they sound like they might come in usefull in other projects aswell.
Many thanks,
OWen
EDIT: forgot to mention the JAN tubes have double ring side getters, is this good or bad? they look pretty cool because the top of the valve is clear.. but how does this affect sound quality?
Many thanks,
OWen
EDIT: forgot to mention the JAN tubes have double ring side getters, is this good or bad? they look pretty cool because the top of the valve is clear.. but how does this affect sound quality?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.