Grundig console amp NF 10

[Pio1980]

Little German jewel from the storage bldg junk pile for an eval after safety check and recap of minor elkos, now playing Vangelis 'Opera Sauvage' directly off a discman's line out thru the Advent Min-E-Waves. How's it sound? Pretty decent tho' this is part of my "playin' around" system and not my 'A' level critical listening system.
http://www.tube-classics.de/TC/GermanTubeHifi/Poweramps/Grundig NF10/NF10.htm

Sine wave test at 1kc gives 18V P/P both channels driven into 8.2 ^ before distortion short of clipping viewed at o'scope. Clipping is reasonably symmetrical and the level nearly identical both channels. Output tubes look essentially unused, no tattooing or smoke rings.
What is the calculated power out please?

 

[Scuzzer]

Let's see, {[(18/2)*.707]^2}/8.2 = 5 watts. I've got it's big brother the NF-20 which is stereo EL84 PP and it puts out a decent 15 watts at clipping. You should be able to squeeze more out of you NF-10. I think they were set up for 4 ohm loads though.

 

[Pio1980]

The site sez they do a bit better at 8^ tho' rated for 4^.
I would seriously love to find an NF 20.

It's probably short due to the original Selenium sandwich stack still being in place, B+ dips from 272 to 234 both channels driven as per above. Suspect a silicon bridge transplant would stiffen it up a bit with a skoshe more beans. The skiz shows the expected voltages at load. The tchoobz would probably last about forever at the lower voltages.
5 watts each from these mini-bottles doesn't suck, abt same as something larger single-ended. What it really needs besides a bit more tidying up is a pair of decent efficient speakers and cleaner source. The source I can do, the speakers are another matter.

 

[Scuzzer]

My Grundig console with the NF-20 has some fairly efficient 4 ohm drivers in it and it tends to get loud quickly. My amp was running the EL84s at 330 volts before I put a bucking transformer in it to knock down the voltage to more reasonable levels. I think it sounds pretty good for an early 60's unit.

I guess I should have read the NF-10 info on the site before I commented. I wouldn't have thought that the amp would be set up for only 8.5W output. Interesting.

 

[Pio1980]

The console was apparently gutted years ago, a bud brought me both chassis and the radio has been a parts donor for a while. The amp I didn't need to part out and so it stayed intact, it also looked like it could be made to work stand-alone. Most of my junk is from the time folks were tossing out consoles, 2nd-string American stereo gear, Japanese and German stuff while looking for the 2 big "M"'s tube gear. I intercepted some of it and piled it up in the storage bldg/junk pile, now it's interesting.
I should say that I'm not mod'ing the NF 10 as it is still a drop-in for a nice console needing one.

 

[derik736]

wanna see where they originally come from??? These were used in some really expensive high end consoles, like my Grundig Schoenbrunn. Back in 1964 they sold them for 3500 german marks, which was almost as much as new Vw Beetle. The entire system includes one Dual 1019 turntable deck (the best model available in 1964), tube preamp with tuner, tube fm decoder and NF10 power amp. Console weight 200 pounds and is 6 feet long. Each side consists of 4 speakers, 12" woofers, oval midrange and two tweeters. I have two of them, one like new and fully working order, another one for parts in my bedroom.
As for the NF10 it´s a really decent sounding amp, well known here in Germany, speacially loved by people using high efficient open baffles with old alnico speakers like Me this amp has some limitation in lower octave, so don´t expect to much below 50Hz, but the rest is pretty sweet.

 

[Pio1980]

Thnx for posting this, I have been curious how it might have been used. There was an Army post near me (I was in the Army and in Germany 3 times from the '60s to the '80s), G.I.s brought German radios and consoles back and they occasionally show up available here tho' I've never yet seen one that large or elaborate. As much as I'm interested in the internals and particularly an NF 20 I'd not want to junk any of them that was restorable.

"this amp has some limitation in lower octave, so don´t expect to much below 50Hz, but the rest is pretty sweet."
The o'scope and a frequency sweep shows this exactly so, I do not know if it can be changed. Certainly there were good reasons to avoid shaking the turntable with low bass response and the speakers and cabinet were limited by practical constraints. Still, good examples of well-balanced overall design..

 

[Scuzzer]

My NF-20 based console looks like this. It was purchased new in Afghanistan by an officer and shipped backed to Denver in '64. It would be a shame to tear one of these apart for the amp and speakers but they're the only real value in the unit.

Spinning some vinyl on the replacement ROK turntable.

Thanks for the picture of the NF-10 console. I don't think I've ever seen one of those.

 

[Pio1980]

MMMM! Me want!!
That is nice!
No reason not to keep these things intact, lo-mid power toob amps are still relatively too easy to come by to scrap these beauties.

I just put 2 1N4007 across half the selenium sandwich as a compromise and the voltages are looking more normal with much better peak power recovery. Output closer to 19.5-20V P/P @8.2^ both channels driven at 40cps. Sinewave distortion starts to appear at ca 60 cps FWIW, 40cps practical lower limit for musical expectations at full power.

 

[Scuzzer]

I agree but you can buy one like mine for $200 or so and sell the amp alone for over $300. Too tempting for your average flipper.

Mine's in great shape, it lived in the same living room in the same spot for 44 years. The only issue it has is that at some point the right channel output tubes melted down and took out the output transformer. They had it professionally rebuilt but the replacement transformer isn't a Grundig. I'll find one of those someday.

 

[Pio1980]

wanna see where they originally come from??? These were used in some really expensive high end consoles, like my Grundig Schoenbrunn. Back in 1964 they sold them for 3500 german marks, which was almost as much as new Vw Beetle. The entire system includes one Dual 1019 turntable deck (the best model available in 1964), tube preamp with tuner, tube fm decoder and NF10 power amp. Console weight 200 pounds and is 6 feet long. Each side consists of 4 speakers, 12" woofers, oval midrange and two tweeters. I have two of them, one like new and fully working order, another one for parts in my bedroom.
As for the NF10 it´s a really decent sounding amp, well known here in Germany, speacially loved by people using high efficient open baffles with old alnico speakers like Me this amp has some limitation in lower octave, so don´t expect to much below 50Hz, but the rest is pretty sweet.

I know how good a decent paper driver can sound, that could be magically musical thru this thing. The good choices would be the easy transparency of vintage AlNiCo plug magnet drivers or a really good single full-range rear loaded high-efficiency driver, or the dynamic drive and punch of a nice horn or constant directivity waveguide based high-efficiency system that doesn't tax it's LF restrictions.

Some observations to non-Europeans;
Many Continentals and Brit Islanders live in "atttached" housing, IE what are known as "efficiency" apartments in the U.S., so both living space and the practical limits of loudness are constrained to a smaller scale than that to which most Americas residents are accustomed. The smaller scale of the table console radios and power output combined with very efficient and sonically well-balanced overall design of these compared to the American console and Hi Fi equipment was more than adequate for pleasurable listenening in these venues. The NF 10's power was as much (or more) as could be reasonable used in most German living spaces, the NF-20's doubled output potential would have been more appropriate to a wealthy person's detached estate house or the American luxury export market. The combination of the efficient speaker systems in these consoles and the spaces in which they were likely to be used made them more than up the task of filling a room with good sound regardless of the apparent relative stinginess of the output ratings compared to the U.S component competition.

 

[Scuzzer]

The combination of the efficient speaker systems in these consoles and the spaces in which they were likely to be used made them more than up the task of filling a room with good sound regardless of the apparent relative stinginess of the output ratings compared to the U.S component competition.

Amen brother! My console doesn't need any extra wattage. If I want ear splitting volume I pick something designed for that task and if I want to hear good music at sane to slightly louder than sane levels the Grundig is a great choice. Heck my EL95 SE/PP (three channels) older Grundig can get loud with just two EL95s. Those Germans knew what they were doing.

 

[Pio1980]

The NF 10 and 20 are very elegant, clean and conventional beam tetrode P/P amp modules. However Grundig could be interestingly creative with their output ckts, you saw the Canadian Grundig Fleetwood thread.
http://www.audiokarma.org/forums/showthread.php?t=292763

Have you seen this attached Grundig ckt? I worked on an export table console for a friend using this unusual 3-OPT/3 channel/2 OP tube arrangement. I thot I knew basically how it worked but seeing the basic skiz helped to fully understand it. Note that it works either single-ended class-'A' stereo or class-'A' P/P mono with a simple switch-over. Pay particular attention to polarity phasing at the outputs.

 

[derik736]

I just connected my console a few minutes ago (just moved in to new flat). Anyway, i´m considering myself as a "hardcore open baffle with old alnico speakers listener" i use vintage alnico woofers from 1960s, originally used in cinemas, manufactured by TESLA (formal Tschechoslovakei) and the rest of my system are mainly saba speakers in open baffles. For some of you not knowing saba speakers: these babies rock!!!! Best midrange you can get, period.
Well i just connected by experimental speakers to my console. I will post a movie about it on youtube.
All i can say: i´m deeply shocked. I was wrong writing about nf-10 not having bass under 50Hz. Well everything is there. YOu just need proper speakers. My tesla woofers are 8 ohm and 100db/1W, so nf-10 has more juice then i need.
On youtube you can see the entire system playing Katie Melua. Speakers are ugly but don´t let that f@%k you up, optic doesn´t really matter in this case and i´ll build new baffles soon. I plan to build something visually similar to Shindo Latour and power it up with nf-10.
I have two nf10s and two consoles, one of them complete,t the other one for parts. I tell you, these are probably most underrated pieces of audio gear right now. YOu can get them for almost nothing. I can´t understand why people pay 200 eurojust for nf-10, since you can buy complete console for 20 euro or so. I bought one almost complete, without TT, for 10 euro. The other one in mint condition was 350 euro but it is like new. Considering, you are getting vintage a-class tube amp, tube preamp with tuner and a pair of 4way speakers, this is a real bargain. Am i right???

 

[derik736]

here she is:

http://www.youtube.com/watch?v=dkwYcpxq-4k

 

[Scuzzer]

Am i right???

Yes, you are right. The NF-10/20 consoles aren't that plentiful over here but they're still relatively cheap considering what's inside them. Thanks for posting the video.