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Recs for Tubes & tweaks for HH Scott gear

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Posted on April 15, 2017 at 12:16:08
CNemo
Audiophile

Posts: 9
Joined: February 15, 2005
 Have had LK 150 amp LC21 pre-amp pair in a 3rd system. Love the midrange, dynamic range, and layering (front to back separation and instrument placement) of the sound stage that it does.

Disappointed in poor frequency extension in the base and rollEd off highs. Was wondering if anyone had experience with these or similar amps and could recommend tubes or other tweaks to improve the sound.

Pre amp uses six 12A7X and one 6X4. Have 4 Sovtek and 1 telefunken + 1 Realistic holdovers from the old days in now.

Amp uses two 7199 phase inverteters, four 6550 output, and two 5AR4 rectifiers. Have nos 7199 RCA inverter and JJ 5AR4 rectifiers in now. Have new Russian Tung Sol 6550s in preferring them to SED 6550 and Sovtek KT 88s that I rolled through.

Have used primarily w budget Morrow MA1 interconnect and SP1 cables and budget bookshelf speakers like Athena BS1, Infinity Primus 140, and Epos ELS8.

Thinking of trying new Russian Mullard KT88 output tubes. I'd appreciate any tube new or NOS or other recommendations that anyone out there might have.

Thanks,
CN

 

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RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 15, 2017 at 13:50:18
Thermionic27609
Audiophile

Posts: 411
Joined: March 29, 2009
 I think the first thing someone advising you would need to know is what sort of condition the amp is in to begin with. What standard maintenance issues have or have not been dealt with?

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 15, 2017 at 17:32:37
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 What Therm said is correct.You need to know the condition of this amp and preamp because keep in mind that these two pieces of gear are 52yo at least and throwing tubes at it probably won't correct your issues.
I would change the coupling caps in the amp to start with as there are only four of them.Pull the bottoms off amp and preamp and see if the caps say American Radionic or are black with yellow lettering.If they are,they should be changed to a paper in oil,teflon,or a good film and foil cap.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 15, 2017 at 17:35:26
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
 Trade up for a Scott Philharmonic?

 

You mean like this?, posted on April 15, 2017 at 18:27:15
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 "
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 15, 2017 at 20:43:26
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 In addition to the well documented advanced age maintenance items, try a high quality modern preamp. Attempt to isolate the sonic defect source.


Eli D.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 16, 2017 at 04:17:19
Uncle Mike
 I use the same amp, actually two, one restored to original (for the most part) spec is paired with a 121-a preamp for an all Scott system. I bought both together from one of the fellow inmates and it seems right to keep them together.
If both of your pieces have not been completely gone over cleaning the switches and replacing all electrolytics, Cera-cap coupling caps and carbon comp resistors (the obvious has to be eliminated as posted by others), you owe to yourself to do so.
The LC-21 you probably know was a kit pre-amp designed to make a quality offering at an affordable price so you're at the mercy of the builder's capabilities. It is based on the front end of the 299 integrated amp(or vice versa depending on how you look at the timeline). This was designed to do journeyman's duty as a rugged all around design. There are tweaks you can make to improve it but it has limitations.
While you have your LC-21 out for maintenance try Eli's suggestion of a modern preamp. Let us know how it works out.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 16, 2017 at 06:33:30
Thermionic27609
Audiophile

Posts: 411
Joined: March 29, 2009
 Looks like two of the 12AX7s in the LC21 are there only for Derived Center Channel and Phase Reversal -- but need to be there because the 12AX7s all use series-string heaters.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 16, 2017 at 07:05:04
Uncle Mike
 Are you sure? I see 1/2 of 6 used for A channel and the other is the center channel.

 

Maybe Mr9iron will chime in...nt, posted on April 16, 2017 at 07:07:16
Uncle Mike
 nt

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 16, 2017 at 07:49:27
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 FIRST let me say I agree with what has already been said. Both units most likely need a good restoration and upgrading.

Typically if you have a roll off problem or "tone" type problem the issue is usually found in the smaller tubes. And you will get the greater effect of tube rolling - rolling those tubes.

Your amp uses 7199s so not much flexibility there! But your preamp uses 12AX7. You could try a set of Gold Lion B759s. They are just as good if not better then the famed RCA black plates. EXCELLENT extension and tone.

If you want to still go with better outputs then go with the Gold Lion KT88s. Excellent tube and they have a lot of energy on both top and bottom as well as still maintaining a good midrange.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 16, 2017 at 21:35:23
CNemo
Audiophile

Posts: 9
Joined: February 15, 2005



Thermi,Mike, Uncle Mike, and Eli

Thanks for all the posts and good suggestions. A little more background for you all.

Both units have been to a tech who gave them a pretty good going over with a minimalist approach replacing things, trying to get things back to original spec, and replacing as little as possible and trying to keep the unit as close to original stock as possible. Pic of some of the work around the amp right Channel is posted as an attachment

Looked over his notes from the repair slips, and he replaced about a dozen caps, half-a-dozen resistors, and the power transformer on the amp. Pre was in better shape and only about 6 caps replaced there. I opened up the bottom of the amp took a quick look around this morning and there were some old Ceracap and old big black Sprague capacitors with red lettering still in there. It should be in decent shape and his run Fairly reliablly every year too, but there is probably still more that can be done to improve both reliability,function and sound.

I we'll try mixing and matching these with other amps and preamps,but it may take me a while to get to that. A decent set of matched output tubes on the pre may also help, but will wait till I try some things with different amps and preamps before investing in any new tubes.

Would appreciate any additional thoughts any of you or anyone else out there may have about things to check out and think about forgetting the gear sounding a little bit better.



Thanks, CN

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 17, 2017 at 04:44:09
Uncle Mike
 The Cera-Caps Must go, they are known to fail and are way past their prime. The electrolytics should only be in the power supply and replaced if not already done. The power supply rectifier is long overdue (probable a Siemens) if it has not been replaced. The ones halfway down in the link are good. A note on replacing the recitifier: because a new one is more efficient than the old a dropping resistor will need to be added after the new rectifier to bring the voltage back in line. I would replace the "black beauty" caps as well. A nice mix of 716p orange drops and K40y PIO
for coupling works wonders.
Honestly you are limping things along and not getting the full benefit. So your assessment is not based on a good unit. Replacing tubes now would not give the most benefit because the rest is lacking. I know costs can be a concern especially if you are paying a tech to do the work. However if you go in with a plan as to what you want done you can manage costs.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 17, 2017 at 08:03:20
bean
 Honestly, nearly every Scott pre I have head just sounds too "vintage tubey" for my liking. But for some reason - not of my making - my Scott 355 tuner/pre just sounds better than any other Scott pre I have listened to. I don't specifically know why, but it had been re-capped before I got it, including caps in the signal path, and a handful of metal film replacement resistors. Haven't opened it in ages, was the early years of my DIY-ing, so I don't recall specifics.

Not sure if the tech was going for best sound or just updating it; it came with the crappiest Chinese '90s era 12AX7s I have ever heard. He had likely had harvested the original Teles.

I'm not much of a tube rolling, but those Chinese tubes forced me; my particular example sounds best with Tele smooth plates in the linestage section, and Mullards in the phono.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 17, 2017 at 18:29:52
Thermionic27609
Audiophile

Posts: 411
Joined: March 29, 2009
 From a certain point of view, most speakers in the 1960s weren't yet full-range, so if you could, for example, improve a circuit's stability by sacrificing a little HF extension or save a little money on a transformer by making some compromise on bass response, it probably made sense. Driving speakers beyond their operational bandwidth heats them up without any particular sonic benefit.

 

RE: Recs for Tubes & tweaks for HH Scott gear, posted on April 22, 2017 at 10:10:43
CNemo
Audiophile

Posts: 9
Joined: February 15, 2005
 All,

Thanks for the tube and other advice. I think Uncle Mike had the best assessment in his reply of Apr. 16 2017 and that the significant number of original parts that are still in there are the biggest issue and keeping the unit s from their full potential.

If anyone has additional ideas or recommendations on replacement caps or parts, tubes, or anything else for the unit, please chime in

It will be a while before I get the time and courage to dig into upgrades myself or the money to have someone else tackle it since the best next step is more than simple tube upgrades and Tweaks.

I'll update this thread or start a new thread when I get into the work and upgrades.

Thanks again to all for your comments and wealth of good advice.

CN

 

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