The Other Side: Tube HiFi Stereos

[Cantplay]

Triode Electronics makes one of the best ST-70 kits.

John

[Teleguy61]

98-102db is pretty efficient for speakers. You should be good at that level.
As other posters says, one of the good things about the St-70 is there is a lot of info and parts available.
For example:

http://shop.ebay.com/i.html?_from=R40&_ ... Categories

[David Root]

bcmatt, I would go with the EF86/12AU7 option myself, and I think you said it best about modern EF86s when you said you should probably buy two NOS RFTs. EF 86 can be microphonic, even NOS sometimes. 12AU7 OTOH is indestructible.

Triode E. offers JJ and Winged C EL34s. No contest, you get what you pay for. Winged C are the only current production EL34s that hold up and sound good IMHO. I had a pair of older Winged C (2002) in my '77 Marshall 2204, they matched real well with the Beijing Mesa STR 12AX7s.

I hate to say it but when it comes to EL34s, the Mullard Xf4 is probably the lowest cost hifi EL34, other than the RFT, which is a LOT cheaper. Oh, I forgot about the Tesla EL34, pre-JJ product, same factory, '70s and '80s are good. You want pre-Bosnia war product. Most folks like them better than RFTs.

[Ian444]

Just for info, if you want to go for something smaller, like 4 x EL84, Tubelab has a PCB and parts kit for $110 for a wonderful little amp, with tube rectifier. You have to source your own tubes, trannies, case and hardware. Definitely amongst the top contenders in the EL84 class. Pic of mine below.

But it looks like ya set on a ST-70 and that would be a pretty impressive piece of gear. I use speakers around 85dB and plenty loud enough for me, even with 6W per side (the Tubelab amp is around 15W/side). I did the opposite to OP, started on hifi and now working on guitar amps.

http://i198.photobucket.com/albums/aa16 ... ePP1-1.jpg

[renshen1957]

Hi everyone,

Most "older" people (myself included) who either didn't have the cash when bitten by the audiophile bug or didn't purchase esoteric speakers such as Electrostatic, Ribbon, Planar, etc. generally do not have very large and powerful amplifiers for home use to listen to music at Concert hall levels.


The general public usually listens at sound levels through their stereos on average of about 1 Watt or less. An EL 84 PP amp is pretty darn loud if dimed through even inefficient speakers.

Quantity of sound does not equate to quality of sound.

Just for info, if you want to go for something smaller, like 4 x EL84, Tubelab has a PCB and parts kit for $110 for a wonderful little amp, with tube rectifier. You have to source your own tubes, trannies, case and hardware. Definitely amongst the top contenders in the EL84 class. Pic of mine below.

But it looks like ya set on a ST-70 and that would be a pretty impressive piece of gear. I use speakers around 85dB and plenty loud enough for me, even with 6W per side (the Tubelab amp is around 15W/side). I did the opposite to OP, started on hifi and now working on guitar amps.

http://i198.photobucket.com/albums/aa16 ... ePP1-1.jpg

The whole point of power in a HiFi system is for clean headroom without distortion, especially during transients (see below) and when a loud low pitch tone requires circa 1 ohm to drive a speaker (a 8 ohm speaker is variable load, FWIW)

Even 1 Watt continually through a 85 dB speaker is loud, and considered threshold of dangerous sound levels by some governmental agencies. Actually, I would say that 90-95 db is closer to the mark, but Osha et al. went with a conservative number. (See below)

I am surprised at no mention of the williamson amplifier in its original lower power form or the Ultra Linear improvements; (UL connections have been found to have higher distortion on the first 1W) or the tonal Nirvana of 5-10 watt amps, or minimalist designs based on triodes such as 2A3 or 300B (however these can be very expensive).

I don't need remind anyone that a hifi systems come in a variety of shapes and sizes, from dual the above mono block SE systems with Triode or Triode wired tetrode or pentode (at lower power than we usually associate with the tubes), to nano amps using subminiature tubes) Power tubes ( and Higher power tubes) were used for their linear properties, and not so much volume. Higher power tubes were also part of the equation for driving power for speaker systems which are not the usual woofer/tweeter combo.

The 6550 and the KT88 have guts, but the 7868, the 7591, and the 7027A were also used for their linear properties (not easily pushed into distortion).

My main (and only) stereo rig is a "The Fisher" pro series X-202 C (two channels each fueled with a separate 7591 PP) not very high powered, however the sound stage, separation, presence, and interior detail is fantastic. This would be the integrated amp I would build, based on sound, but it is a complicated amp (read expensive).

I would look into a simpler design, using a 6SN7 (octal equivalent of a 12AU7, why send a little boy when you could have his father do the job) for preamp tube, a hifi version of a schmidt splitter, and yes you can have EL84s check out http://diyaudioprojects.com/Schematics/ ... ematic.htm

For Stereo, I think I will state the obvious, you will need two sets of OTs.

FYI, The original Sunn Amps (which had a brief endorsement deal with Jimi Hendrix until he played through them and bailed on the deal are actually the Dynaco circuit (and iron); the Sundholm brothers (one briefly the bassist of Kingsmen fame) ripped off the design to build Bassamps. Fender purchased Sunn amps and shut production down in 2002.

As to sound:

Normal conversation (3-5') 60-70dB (unless your wife is from China, gets louder when involved in a conversation or angry 90+db.)

Telephone dial tone 80dB (old school bell)

Train whistle (train air horn) at 500' 95db
(my Mofo ex-backyard neighbor had a dxmn blasted train air horn for his RV connect to a hair trigger alam system 150' from my bedroom window. SOB, would also hit the panic button everytime his favorite team scored on TV, yes I called the Police on him)

Level at which sustained exposure may result in hearing loss 90 - 95dB

Power mower at 3' 107dB
Snowmobile, Motorcycle 100dB
Power saw at 3' 110dB
Sandblasting, Loud Rock Concert 115dB
Pain begins 125dB
Pneumatic riveter at 4' 125dB
Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection 140dB
Jet engine at 100', Gun Blast 140dB
Death of hearing tissue 180dB
Loudest sound possible 194dB

Normal piano practice 60 -70dB
Fortissimo Singer, 3' 70dB
Chamber music, small auditorium 75 - 85dB
Piano Fortissimo 84 - 103dB
Violin 82 - 92dB
Cello 85 -111dB
Oboe 95-112dB
Flute 92 -103dB
Piccolo 90 -106dB
Clarinet 85 - 114dB
French horn 90 - 106dB
Trombone 85 - 114dB
Tympani & bass drum 106dB
Walkman on 5/10 94dB
Symphonic music peak 120 - 137dB
Amplifier rock, 4-6' 120dB
Rock music peak 150dB


Best Regards,

Steve

PS script the JJ KT77 were back engineered from a NOS tube, and are an excellent replacement for the EL34, higher headroom and more durable. However, nothing to my mind beats a NOS (if ya got the money). Some of the newer offerings may not measure up to NOS stock, but the quality has improved at the audiophile level (if ya got the money).

[galtjunk]

I have an old Dynaco ST70 with 4 Mullard el34's and an H.H. Scott Stereomaster with 4 7591's.

I use the Dyna. I'll probably build something out of the Scott.