Tube rolling for the Scott LK-48

rajacat · « **on:** 21 Jan 2007, 05:19 am »

I've had my freshly restored Scott LK-48 for about a month and now getting the urge to do some tube rolling. The present complement of tubes consists of a RCA R54 GYB brown base, (2) Telefunken 6U8A, I think, because the lettering has worn off, (4) Telefunken 12AX7,
(4)Ei EL84EG Yugoslavian tubes.

If anyone has some experience related to tubes for the LK-48 or any other of the closely related Scott integrated amps, that they would care to share I'd appreciate it greatly.

Thanks,

Raja

Songforyou · « **Reply #1 on:** 21 Jan 2007, 05:33 am »

Hi Raja,

I have a Scott 222c that has been modded by Mapleshade. I bought it with Electro-Harmonix el84s. When it came time to change tubes, I bought a quad of the highly regarded JJs. Sounded like crap. Everything slowed down and turned to mush. Went back to the Electro-Harmonix and everything fell back into place. Better highs and much better bass. These are not expensive tubes. I haven't tried NOS because I haven't seen the need to.

I'm not trashing the JJs at all. They probably work well in other amps, but in the Scott they are just too rich.

rajacat · « **Reply #2 on:** 21 Jan 2007, 05:52 am »

Hi Song,

I should probably add to my post that 7189's are specified for the LK-48 but EL 84's work too. Thanks for the info. I checked and Electro-Harmonix 84's go for about $20/pair which is very reasonable. I wonder if your Mapleshade mod, which is very extensive, changes the response and charactor of the tubes from the stock Scott.

Raja

Scott F. · « **Reply #3 on:** 21 Jan 2007, 02:10 pm »

Hiya Raj,

I'm not quite sure what Mapleshade does in their mods to the Scott but I know what I did to my 299. One of the first things is to change out the old selenium rectifiers. You may want to consider doing this (or having it done). Not if but when one goes bad, it will take out all kinds of surrounding parts in the power supply costing you even more money on repairs.

The other thing most of the guys do is replace the coupling caps and power supply caps in the unit (including tone control caps). This really cleans up the 'sound' of the units. They become much cleaner and more 'accurate' sounding (at a loss of the romantic 'tube sound'). One of the other things to want to do is change out the old Allen Bradley resistors that have seen the most stress over the years. These too will have an effect on the sound. The noise floor drops dramatically and the unit again sounds even cleaner.

These are marvelous sounding amps. I've owned one for many years and still love to listen to it. One of my all time favorite tubes is the EL84 (7189, 6BQ5). In push pull they don't produce much power but boy can they make a pair of speakers sing. Far better than many of the higher powered tube amps I've had (or have). In fact I'm listening to the Jolida 102b (el84 PP) driving a pair of Aperion 632 monitors right now and it's a marvelous combination.

Not sure if you've found out about this site yet but Lee Shuster runs the HH Scott site and forum.
http://hhscott.com/
There is a wealth of information and resources there.

Also, if you don't want to tackle the rebuild yourself, Craig at NOS Valves is very reasonable. I've not used him before (as I do my own repairs) but I have talked to him and he is defiantly on top of his game.
http://www.nosvalves.com/index4.htm

rajacat · « **Reply #4 on:** 21 Jan 2007, 06:27 pm »

Quote from: Scott F. on 21 Jan 2007, 02:10 pm

Hiya Raj,

I'm not quite sure what Mapleshade does in their mods to the Scott but I know what I did to my 299. One of the first things is to change out the old selenium rectifiers. You may want to consider doing this (or having it done). Not if but when one goes bad, it will take out all kinds of surrounding parts in the power supply costing you even more money on repairs.

The other thing most of the guys do is replace the coupling caps and power supply caps in the unit (including tone control caps). This really cleans up the 'sound' of the units. They become much cleaner and more 'accurate' sounding (at a loss of the romantic 'tube sound'). One of the other things to want to do is change out the old Allen Bradley resistors that have seen the most stress over the years. These too will have an effect on the sound. The noise floor drops dramatically and the unit again sounds even cleaner.

These are marvelous sounding amps. I've owned one for many years and still love to listen to it. One of my all time favorite tubes is the EL84 (7189, 6BQ5). In push pull they don't produce much power but boy can they make a pair of speakers sing. Far better than many of the higher powered tube amps I've had (or have). In fact I'm listening to the Jolida 102b (el84 PP) driving a pair of Aperion 632 monitors right now and it's a marvelous combination.

Not sure if you've found out about this site yet but Lee Shuster runs the HH Scott site and forum.
http://hhscott.com/
There is a wealth of information and resources there.

Also, if you don't want to tackle the rebuild yourself, Craig at NOS Valves is very reasonable. I've not used him before (as I do my own repairs) but I have talked to him and he is defiantly on top of his game.
http://www.nosvalves.com/index4.htm

Hi Scott,

I've already had Ryan Inman @Hot Glass Audio refurbish my LK-48 and it appears that he replaced the capacitors and some other stuff. Ryan basically restored my Scott to factory condition with no mods whatsoever. He told me that the stock circuit was perfect as originally designed and unlike some of the other Scott models it needed no major changes to operate optimally. The Mapleshade refurbish/mod disables most of the controls and does a massive reworking of the whole amp. From what I understand,
all of the knobs on the facepiece are rendered inoperative except for the on/off volume switch.

I'm familiar with the HH Scott site. It's huge although sometimes I find it a little hard to navigate.

BTW what rectifier tube do you use? Have you used headphones with your Scott? Also have you used the Scott's phono stage? Ryan says that it is superb, the LK-48 version that is.

So far I prefer the sound of the Scott to the Gainclone/Mapletree pre combo.

Raja

Scott F. · « **Reply #5 on:** 21 Jan 2007, 06:42 pm »

I completely agree, the stock circuit is just fine the way it is. The amp only needs some fresh parts after all these years and Ryan is another one of the guys I would trust to do the refurb.

When it comes to the rectifier tube, I generally listen to the Mullard GZ34. I know it's one of the most expensive ones out there but it really does sound the best. Same goes for the Telefunkin 12A series tubes and the EL84 output tubes. The Bugle Boy EL84's are really nice sounding too, but again expensive.

On a budget, the EH tubes are darned fine sounding. I think I saw a thread on the site here where some one was selling EH tubes that had been cryo'd for like $3 or $4 dollars over what they normally retail for. I'd be tempted to try those. that would probably take that last bit of edge off the EH's.

Brad · « **Reply #6 on:** 22 Jan 2007, 01:50 am »

I agree with Scott on the rectifier tube.

My 222 still has the stock preamp tubes and I'm using 7189's.
The Mullard rectifier made a noticeable difference in improving the sound.

Scott F. · « **Reply #7 on:** 22 Jan 2007, 02:00 am »

Hi Raj,

I haven't tried headphones with mine though I guess I should.

The phono stage is very good. It holds its own with a lot of stand alone stages I've played with over the years.

rajacat · « **Reply #8 on:** 22 Jan 2007, 06:44 am »

Well I guess I'll start looking for a Mullard rectifier tube. The Telefunken's are supposed to last for many years and stand up well as far as their sonic properties so I won't be rolling them any time soon. The Ei EL84EG's with the gold plated pins seem to be middle-of-the-line so I will wait awhile before I concern myself with replacing them.

Raja

Songforyou · « **Reply #9 on:** 22 Jan 2007, 07:26 pm »

Hi all,

I can't speak to what Mapleshade does in technical terms, but yes they do bypass all the front panel functions (the tone controls, balance etc.). Volume, source selection, and tape monitor are the only ones that work. They claim it contributes to greater clarity, but I haven't compared mine to a stock unit.

What I can say is that I had it in for some additional work in a shop in Toronto (the Audio Zone folks) and they were impressed with the mods and thought the amp sounded great (they also agreed that the EH EL84s sounded much better than the JJs in this amp).

One of my complaints was that the headphone jack is noisy (hum that increases with volume). It's a damn shame too, because it sounds far better than my Musical Fidelity X-Can driving my Senn 600s. One thing about the stock headphone jack: it doesn't cancel the speaker output. You have to disconnect the speakers when you listen to phones (that's my understanding, anyway).

I do have original telefunkens in the phono stage and they work great with my Scout/Dyna20H. You are limited to MM or HOMC though.

I can't believe how good this thing sounds. I've had more expensive gear in the house, but the Scott sound is something special as far as I'm concerned.

Scott F. · « **Reply #10 on:** 22 Jan 2007, 07:33 pm »

Hey Song,

Just a quick word of caution regarding the headphones. Don't disconnect the speakers and turn your Scott on to listen to headphones. Tube amps need to see a load (as in speakers). Otherwise you will burn up the output transformers which would really suck. You can disconnect the speakers if you install an 8 ohm, non-inductive resistor (10-25 watt) in place of your speakers.

Brad · « **Reply #11 on:** 22 Jan 2007, 08:26 pm »

Quote from: rajacat on 22 Jan 2007, 06:44 am

The Telefunken's are supposed to last for many years and stand up well as far as their sonic properties so I won't be rolling them any time soon.
Raja

My Telefunkens are stock - 40+ years

rajacat · « **Reply #12 on:** 22 Jan 2007, 08:41 pm »

It looks like mine are stock too! I imagine that the 'funkens would have fetched more $'s on 'gon than what I (before refurbish) paid for the Scott at a garage sale.

It seems that these Scott integrateds have some of the best SQ per dollar spent in the world of integrated amps.

Raj

Brad · « **Reply #13 on:** 22 Jan 2007, 08:47 pm »

I saw a lot of Fishers being parted out on ebay when I was looking for a Scott.
Kind of a shame......

Here's a link to the Scott owner's manual.
Pretty interesting read:

http://hhscott.com/pdf/64_amp_manual.pdf

rajacat · « **Reply #14 on:** 22 Jan 2007, 09:07 pm »

Hmmmm.....for some reason the download of the owner's manual was not successful.

Brad · « **Reply #15 on:** 22 Jan 2007, 09:52 pm »

Their server isn't the fastest - and the file is appx 20mb
I can email it to you if you send me a PM.

Hot Glass Audio · « **Reply #16 on:** 31 Jan 2007, 07:38 am »

Quote from: Scott F. on 22 Jan 2007, 07:33 pm

Hey Song,

Just a quick word of caution regarding the headphones. Don't disconnect the speakers and turn your Scott on to listen to headphones. Tube amps need to see a load (as in speakers). Otherwise you will burn up the output transformers which would really suck. You can disconnect the speakers if you install an 8 ohm, non-inductive resistor (10-25 watt) in place of your speakers.

Every H.H. Scott amplifier is 100% unconditionally stable into any load, or no load at all. The amplifier cannot be damaged by operating it without a load (even at 100% volume).

The later models (299-D, 222-D, 233) featured a speaker on/off switch and 1/4" phones jack, and these are more convienent to use with headphones (as you can manually switch off the speakers).

Note that all Scotts use both a voltage and current feedback loop, hence their remarkable stability. The output transformers are never in any danger, and this combination of feedback eliminates the risk of "inductive kickback" to the primary winding, and the subsequent oscillation that would follow.

Hot Glass Audio · « **Reply #17 on:** 31 Jan 2007, 07:54 am »

Regarding tubes for the 7189 based H.H. Scott models:

(1) Russian 6pi14pi or 6pi14pi-EB are the best two modern production tubes to use. They are sold under the generic form, or as "Sovtek" and "Electro-Harmonix". The early 1980's production seems to be very consistant from tube to tube.

(2) JJ EL-84 - The second best choice for modern production EL-84's

(3) Ei EL-84 - Avoid these at all costs. The tubes cannot handle the dissipation requirements of the 299-299-B-222-C-222-D models.

The average Scott applies 420V to the plate, and 390V to the screen, with an average cathode current of 44 mA per pair of tubes. Each tube dissipates roughly 9.2 W at idle, or
77% of the maximum rating for a 7189/EL84. Provided the tubes are well matched-balanced-biased, this is a very conservative operation. The only modern tube that cannot carry its weight is the Ei/Yugo EL-84.

I'd agree that the Mullard or Amperex 5AR4 is the best (certainly from a reliability standpoint). Buy a new one and chances are it will outlive you! Or, you could pay $11.99 for a Sovtek every year (they typically only last for one year). Avoid the JJ version all together (leakage).

Scott F. · « **Reply #18 on:** 31 Jan 2007, 12:28 pm »

Hi Ryan,

I was not aware that the Scott's were designed to to be able to run without a connected load. Good info

Brad · « **Reply #19 on:** 31 Jan 2007, 03:50 pm »

Hey Ryan,

Welcome to AC. I didn't realize you had joined.
Thanks for the info on the 6pi14pi tubes.....will come in handy.