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A Roberts 1650 Reel to Reel followed me home from the local GW. The tube line-up is 6CA4 rectifier, (1) 12AT7, (2) 12AX7s and (2) 6BM8 EL82s. I brought it up and using a CDP as input and it all worked. Now, What do I do with it? My thought was to make a small, compact office/bedroom system with it driving some 4 inch "full range" speakers and a secondary powered sub. I'm only a beginner here so be nice: I assume the 12AT7 is a phase spliter and the 12AX7s are inverters. Would this amp be using both parts of the 6BM8? Is there a schematic for this arrangement that someone may have for me to look at and study? Should I stick with this design or is there a better way to use this amp. Is it capable of somewhat decent high fidelity? My plan is to scavenge parts and rebuild it with new capacitors, etc. I do not think the R2R is worth much for a collector.
Thanks,
Dave
Follow Ups:
Hi Dave.I've disassembled a couple of tube tape recorders, and the parts generally do make very nice low power amplifiers. What I find is that the OPTs are often quite small, usually resulting in an amp with not much deep bass, but beautiful clear mids and highs. Should work well along side a quick, punchy sub.
Valuation-wise your Roberts could be worth anywhere between $10 and $100 depending on condition and buyer desire. I recently sold an Akai (same manufacturer) about like it for $35 at a swap meet. Some of the later solid state Teacs and (what was their pro brand?) still sell for hundreds of dollars, but most of the older consumer stuff isn't worth much.
Since non-functioning tube amplified tape decks can often be had cheap or free I've been hoping to find a better use for the iron than "another low powered SE amplifier". It is the same issue many of us have experienced with small console amp OPTs. May try some experiments using a couple small OPTs in series, or possibly as plate chokes (again, in series). If anyone has any good ideas I'd like to hear them.
6bm8/ecl82 is a dual-section tube with a separate triode & power pentode within the same bottle. 12xx7's are dual-section too, with 2 separate triodes in the same bottle. Discover tube pin-outs at the link below. Now, you can draw your own schematic from observation if none is found on-line or in your public Library. As already mentioned, the 6bm8 triode section likely is a driver for it's pentode section, & the 12xx7's provide pre-amp gain stages. My stereo 6gw8/ecl86 (cousin to the 6bm8) uses 4 such tubes with the triode sections providing driver & splitter for the push-pull pentode output.
Nice site. I bookmarked it for future use.
Seems like I can make a nice, simple amp from the parts.
Dave
BTW, 6bm8 is the American type designation for this tube & ECL82 is the European equivalent type designation. If the words Gt Britain immediately follow the ECL82, that indictes the European (or Mullard) type equivalent & DO NOT mean made in Gt Britain.
Audio Xpress magazine, volume 36, number 2 (February 2005), in an article written by Aren van Waarde, presented a wonderful little 6BM8/ECL82 based stereo single-ended project. It is worth checking out. I believeAudioXpress.com
could be a source for a back issue.
I checked the audio xpress website for back issues. In March 2005 they list an article titled "A Minimalist Amplifier Design". Would this be the correct article? The Feb 2005 issue had an article on a preamp but I did not see the amp. I can order the whole year on CD but I just wanted to make sure it was the correct one. OR.. Do you have a copy I could get from you?
Thanks,
Dave
The article is listed as "A Study Sytem, Pt. 1", in the February 2005 issue, and begins on page 6.
1650 isn't listed in the Sams index.If it's stereo, the 6BM8 is used as a single-ended output stage - no phase splitter required - the other half is voltage amp (driver). The tape head needs a LOT of amplification, so 12AX7 is used there, probably also as mike preamp for recording. 12AT7 could be erase oscillator, or could be audio amp stage.
Yes, it is stereo. It is listed as a model 1650/1670. I'll do some searching. The front panel has inputs for two mics, two volume level controls, two VU meters and one tone control. Of course it has play and record settings. The back has 1/4" RCA jack outputs for L&R external speakers (it has two small internal speakers) and std RCA outputs for L&R "extension tweeters". It also has L&R Pre-amp outputs, 1/4" headphone output and RCA input for phono/radio.
Dave
First, get the Sam's manual. Yes, the 6BM8 makes a decent little amp. There are serious audiophiles that still listen to pre-recorded 4 and 2 track R2R tapes that were avaliable in the 50s and 60s. Ray Hughes
"I take you as you are
And make of you what I will,
Skunk-bear, carcajou, bloodthirsty
Non-survivor.
Lord, let me die but not die out." THE LAST WOLVERINE by James Dickey
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