Altec 755E: too many questions

[Tralalalala]

Hello all,

To be honest; I thought this forum was no longer living; after a ( way too ) quick google search I did not find you --I did remember that I joined the forum several years ago and got a lot of help regarding my DIY 612 utility cabinets for my Altec Lansing 604E Super Duplex drivers. My Duplexs are no longer in my possession , with a much too low WAF, and still not having the possibility of having a dedicated hifi room...

Today I have a new pair of drivers; I am very eager to learn more about these drivers; a pair of 8" NOS Altec 755Es. I have too many questions, and I have already tried my luck at the lansing heritage forum ( NOS Altec 755E: Q: CABINET / AMP / TWEETER? ) ; after the last replay to my thread, I was redirected here; I am crossing fingers that this will be a more suitable place for my questions.

INFO:
I got my interest in these drivers after seeing on net a pair of reissues of the 755As ( alnico ) from LM Audio; based on the Western Electronics 755A ( see ref for more info about these reissues--I, myself, have no affiliation to LM Audio )

Q1. My 755Es measure 6.6ohm and 6.9ohm; will this 0,3ohm difference in resistance affect sound? The specs on the 755E says 6.8ohm

I will make a cabinet based on the Altec 618. It will be made of high grade pine plywood. All sides in 9mm ( 1/2 inch= 12mm ) so this is by far the thinnest cabinet Ive made, but Ive read on net that some of the original 618 cabinets were made out of 9mm ply. I will rear mount my 755Es. I will reinforce the cabinets as shown at this site / most of my info about how I wanted to do my cabs are from this site: REF: Junkyard Jukebox

Q2: What kind of material should I use as damping / it looks to me that these original 618 units did not have much damping material?

Q3: I have not found / read much about matching between amps and the 755Es. What kind of amplifiers should I consider?

Q4: I have understood that the 755Es do ( need ) work well with different tweeters. I do got a pair of Decca Super Tweeters ( ribbon tweeters ) with a range of 7KHz- 30KHz, Crossover at 7 KHz, Efficiency : 88db at 4W at 1meter. Is this a plug & play unit with the 755Es? ( For the record: I do have very little knowledge about integrating tweeters / subwoofers with my gear. )


All inputs will be greatly appreciated.

[GM]

Greets!

Q1. No.

Q2. 1" OC 703 acoustic fiberglass insulation as shown is sufficient for the 618.

Q3. SET 300B would be nice.

Q4. Big problem is efficiency, so what's the ribbon's?

These look viable: Focal TN-45 - Google Search

GM

[Tralalalala]

Greetings GM !

Thank you :-)

I do not have a 300B SET, but I have a LM3875 Gainclone kit, ( I?m sure I?ve read somewhere way back that it is similar in sound to 300B SET amps--) ; my best bet; will try to find a well matched tube pre for it, since I?ve just recently read more about the subject; that the Gainclones do share many characteristics with tube amps, but cannot replace them.

The Decca Super Tweeter: efficiency is rated to 88dB at 4W at 1meter. How do i calculate how much this equals at 1W at 1meter, something is off--I do not manage to wrap my head around it.

[GM]

You're welcome!

Only auditioned one Class A GC amp, chip preamp system coupled to an impedance matched Lowther DX3? sans rear cover loaded in an Fs tuned MLTL and while quite nice in a near-field app it had none of a SET's 'lushness', just 'squeaky' clean to the point of being 'dry'/'sterile'. In short, what qualifies as entry level 'super FI' nowadays. At least the DX3 added a bit of 'life' to it [euphonic distortion] when pushed to its wide band low distortion limits.

Seriously? Is it missing its horn or.....? Anyway, 10log[4] = ~6.02 dB, so only ~82 dB/W/m or ~10 dB too low. Fine for many cone/dome/monkey coffin speakers, but woefully inadequate for any vintage speaker app I can think of and where you'd need an array of [10]/755 and an 'infinite' array [~70+% of room height] of them/speaker to match up to some Altec, etc., systems.

GM

[Tralalalala]

oh man...

My decca ribbon tweeters are without horns.
Understand.
Not a well suited tweeter for the 755Es

I looked at the Altec H3000 & the EV T350 mentioned here: 755E mating with tweeter ; considering, but from the looks of it difficult to find.

What about this one: for sale locally; Gamma VLD13 ribbon tweeter with horns;
Efficiency: 95dB at 1W at 1m
Impedance: 8ohm
Frequency: 2 600Hz-40 000Hz

Spec sheet can be found here: 古典音響。墾丁大腳牛教練: 03/31/15


*What about low wattage class A amplifiers for the 755E?s?

[GM]

Not enough info to be sure without a response plot, etc., though it's low cutoff implies a heavy ribbon, which would mean it's likely rolled off like a typical relatively large cone/dome tweeter.

'What about low wattage class A amplifiers'

What about them? They're what the 755 and all early drivers were designed for, but if SS, then its power rating needs to be clean up to at least 2x the driver's rating since it won't track its impedance like a tube amp.

FWIW, I once read that a rule-of-thumb back during the transition years was to increase an SS amp's power rating at least 2.5x required by a P-P tube amp and 4x a SET and that at least the first 10 W be Class A, hence the ~universal adoption of Class A-B for studio reference, cinema, HIFI apps.

GM

[mah]

Good price? Focal TN-45 1" PolyGlass Series Titanium Tweeters | Atoz Car Rental REPLY APPEARS AT TOP OF PAGE FOR SOME REASON.


Q1. No.

Q2. 1" OC 703 acoustic fiberglass insulation as shown is sufficient for the 618.

Q3. SET 300B would be nice.

Q4. Big problem is efficiency, so what's the ribbon's?

These look viable: Focal TN-45 - Google Search

GM[/QUOTE]

[GM]

Buy TN-B - Focal Polyglass Tweeters New Pair (Replaces TN-A, TN-47, TN-45) Online at Low Prices in USA - carkart.com

This appears to be the lowest in the USA, but assume its free shipping won't be to 'Down Under'.

GM

[Tralalalala]

Hello GM,
Hello mah,

PM sent to GM.

Is the site stable for its users? I mean: the forum is very quiet, I do not mean necessarily this thread, should I stop posting?
? asking since I have understand this has been an issue for some time ?

I have now received the 755Es, both are in very good condition :-) , and supposedly; I am the third owner; the 1st owner never did finish a cabinet for them and sold them to the previous owner; who has stored them on shelf for many many years. I got my 755Es for approximately 450 USD.

Today I have a NAD 3120 ( 3020B without tone controllers ) and the Quad 303 and 33, both of the Quad units are serviced.

Both high wattage SS Class A amplifiers and 300B SETs are expensive; I want something stable / user friendly; so others than me can use it, most of all something that not has to be ?monitored? when switched on. I guess I am looking for a well suited SS integrated amp.

Earlier I meant low wattage SS class A: like the ACA from Nelson Pass. I got the answer I was looking for; this one has too low wattage for the 755Es.

So how good are the Altec 755Es?I mean : how is its sound signature / matching with 300B SETs are already mentioned, but is there other well suited alternatives it will match?

PS:
I messed up my understanding of Gainclones : I read this article several years ago and mixed most of the points mentioned. At least I found my source? ; op-amp

PPS:
I guess I will wait with tweeters until I have actually listed to the 755Es in a 618 cab.

EDIT: OK, so adding a tweeter is way beyond my skill set. REF: Adding Tweeter to Full Range - diyAudio
Looking forward in listening to the 755Es as originally intended; hopefully I will be happy with the drives when put in 618 cabs :-)

[Phil-G]

the board is hanging pretty well lately, but we still are looking for a host change here.
i like the pair of 755Es i have. they sound really nice. i settled on 2cu ft sealed 618like boxes. they may not have the highs like the 755As but what the do have, they do well. i added a pair of dome tweeters with 5000k high pass filters and an L-pads.
a small sub that goes from 75hz on down helps a lot too.