Greetings and happy new year! I've been learning about valve amps recently and would really like to build a "hifi" stereo amplifier as a project.
I like the idea of recycling old components into something new and have seen a lot of videos on youtube of people doing just that.
I've been offered 2 identical reel to reel tape recorders which are destined for the tip. I'd like to reuse some of the internals to build into a new circuit. Obviously each tape recorder is mono but each has an output transformer so I'll have a matching pair (assuming they are usable for this purpose).
The valves are: ECC83, ECL82, EM84.
Can anyone suggest a circuit that could make use of the parts from the machines? Would I be able to make a stereo amp out of these or would I have to have 2 separate amps in the chassis?
I found a circuit diagram for the tape recorders online:
I like the idea of recycling old components into something new and have seen a lot of videos on youtube of people doing just that.
I've been offered 2 identical reel to reel tape recorders which are destined for the tip. I'd like to reuse some of the internals to build into a new circuit. Obviously each tape recorder is mono but each has an output transformer so I'll have a matching pair (assuming they are usable for this purpose).
The valves are: ECC83, ECL82, EM84.
Can anyone suggest a circuit that could make use of the parts from the machines? Would I be able to make a stereo amp out of these or would I have to have 2 separate amps in the chassis?
I found a circuit diagram for the tape recorders online:
You have enough valves to make one 4 Watt amplifier; ECC83 and ECL82.
EM84 is a 'magic eye' used for tuning or as a vu meter.
EM84 is a 'magic eye' used for tuning or as a vu meter.
The part of the schematic you show is the preamp. likely the ECC83. Of more interest is the power amp that drives the speaker, the ECL82. These are triode/pentodes so you could make a small SE amp, ~2 watts, from just this tube (2 for stereo). See attached for Mullard amp. You wouldn't necessarily need to use tube rectification and you could ditch the tone control too. Likely the power trans from one of the recorders wouldn't have enough "juice" for a stereo so you'd have to build two mono amps but they could be in the same chassis.
Good luck, S
Good luck, S
Attachments
If you download the 2nd half of the schematics from https://www.radiomuseum.org/dsp_guest_schema_register-ng.cfm?schaltplan_id=721184 you will notice that the output transformers are wound for a 3 ohm speaker; will work well with 4 ohm speakers but with 8 ohms you get much less power out, maybe just 1 W ...
Thanks for the replies.
So, I can make 2 separate separate amps from the ECC83 and ECL82 with the stero signal split betwer them given me 4w output (2w channel).
That's great. I don't listen to music loud and my listening room is small.
A couple of questions,
as the OT is only wound for 3ohms, is it possible to replace these with ones which would allow for 8ohm speakers to be used?
Also, is there any chance that the mains transformer could provide enough voltage for stereo? How could this be tested/measured to rule it out?
Thanks.
So, I can make 2 separate separate amps from the ECC83 and ECL82 with the stero signal split betwer them given me 4w output (2w channel).
That's great. I don't listen to music loud and my listening room is small.
A couple of questions,
as the OT is only wound for 3ohms, is it possible to replace these with ones which would allow for 8ohm speakers to be used?
Also, is there any chance that the mains transformer could provide enough voltage for stereo? How could this be tested/measured to rule it out?
Thanks.
A basic stereo tube amplifier only needs two ECL82 tubes. You can save the remaining tubes for future projects. ECL82 has been fitted into small record players and tape recorders also because good reference designs published by tube manufacturers such as Mullard were available for free to the manufacturers of cheap consumer products. I attach a fairly detailed version of the Mullard design, from the Mullard Outlook publication - follow the schematich without tone controls. You can use a modern simplified schematic instead, but the 10KHz bandwith is a quite common limitation of the small and cheap output transformer installed on those devices. Just use the transformers you have now. If they don't are up to the expectation, just replace them later. Leave some extra space on the chassis, because modern Hi-Fi transformers are bigger. The original Mullard schematic does use a tube rectifier, but you will use a solid state full bridge rectifier as required by your power transformers. You can build your stereo amplifier as dual mono: put the two channel in the same chassis and use a single stereo volume potentiometer for convenience. The potentiometer value should be between 10K and 100K - the value listed on the original design was meant for a piezo cartridge.
Thanks very much for the ideas. Plenty there to be getting with.
Just have another question if anyone can help....
With regard to the following
Just have another question if anyone can help....
With regard to the following
Would there be any advantage to using the ECC83 at all, maybe following a circuit which uses this as a pre amp?
Just had a look a the EM84's. Might be quite interesting to incorporate these as VU meters. Then again, they might be become a bit annoying after a while 😀
Could a switch be incorporated for these somehow so they could be turned on and off while the amp(s) are running? That would be cool
I'm also swaying towards building these as 2 separate mono block amps as opposed to sharing a single chassis.
Modern sources, DACs and even phono preamps, have sufficient output that an ECC83 stage in the power amp isn't necessary. If you have or are considering a vinyl source the ECC83s could be used in a phono pre. This assumes that the ECC83s are sufficiently quiet enough and non-microphonic for a phono amp.
S.
S.
In addition I'd provide some NFB from the xformer's secondary to the triode's cathode.
To your EM84/VU meter question: Simply get a SPST switch into the plate supply wire to both tubes.
Best regards!
To your EM84/VU meter question: Simply get a SPST switch into the plate supply wire to both tubes.
Best regards!
Some of these old tape recorders had fair quality 'broadband' speakers that had to fill a classroom, so don't discount being able to create a minimalist music player with minimal alterations.
The ECL82, being two tubes in one bottle, is not the easiest tube for a first timer due to the proximity of the different connections. If there are small PCBs in each recorder, you could try and salvage them in their entirety, determine where 'line in' starts, and keep the wring to a minimum.
The ECL82, being two tubes in one bottle, is not the easiest tube for a first timer due to the proximity of the different connections. If there are small PCBs in each recorder, you could try and salvage them in their entirety, determine where 'line in' starts, and keep the wring to a minimum.
The ECC83 tube can be used as preamplifier stage instead of the triode section of ECL82. The amplifier gain will be higher (or the distortion slightly lower) and the component placement will be slightly easier. You will need a bigger chassis and an additional tube socket. The schematic you've found is the easiest to build, but audio quality will be poor with your reclaimed output transformers, because they are really designed for the Mullard schematic with strong global feedback. To add the EM84 level meters, you need a small circuit with a diode to rectify the audio signal and maybe a transistor to increase the level. If the white side of your reclaimed EM84 tubes is not pristine and flawless, the EM84 tubes may be weak and barely working. This tube was the first to go out of service. The loudspeakers of your tape recorder should be 8 x 5 inch in size: a good vintage midrange speakers.
Sounds interesting. It might make sense to use the ECC83 as I already have them and the sockets.
do you know of a diagram which exists for that circuit?
Thanks
Download the RCA receiving tube manual. At the end there is a section called "resistance coupled amplifiers". You will find the master schematic of a very basic preamp stage and several tables with suggested component values for many audio tubes. Check out the 12AX7 values, this is the RCA name for ECC83. If I understand correctly this is your first tube build, so it is best not to wander too far from the main path.
Just be cautious it is not just 'plug and play'. A lot of skill and knowledge are behind all circuits. If you can redeploy the contents of the tape recorders as modules, you can get something working a lot easier with fewer changes, and then start there with bigger changes and adaptions.
I would not try to reuse the tape recorder circuits. Those portable open reel recorders from the '60 targeted to the home market are not hi-fi devices with clear circuit separation. They have a big, complex play/record switch (seldom working anymore) that completely rearranges the tube functions, because they needed to sell a product with only two or maybe three tubes. The schematic diagram is hard to decode. Component values and quality are the bare minimum required. Hum was just a given. There is a reason why the collector value is so low, compared to tube radios and other tube gear of the same age. It is best to just grab the good parts and build new.
If you decide to build from scratch, there is this very neat build for a SE ECL82 from a contributor here, Stephe ...
6BM8 (ECL82) SE
She created a video series of the build, so a perfect starting point!
6BM8 (ECL82) SE
She created a video series of the build, so a perfect starting point!