|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
173.28.79.16
Hey, I'm a longtime AK user but decided to join AA as well after seeing the extensive discussion of the Sherwood tube equipment in this forum. I own the much-lauded 7189 S-5000 with the slanted preamp tubes. So far, I've recapped it to stock specs, replaced the selenium with silicon and added a global bias adjustment. The thing sound phenomenal, but I see a lot of discussion about modding this amp around here. Is there some kind of schematic or general writeup of these mods? Also, has anyone had any luck replacing the volume pot? Mine has really poor L/R tracking and it's kind of annoying fiddling with the balance pot all the time.
Follow Ups:
A bit late to the discussion, but I have compiled most of the S-5000 mods from previous post here on the asylum. You can email me If you'd like copies.
Freak out...Far out...In out....
The 7199 has gone the way of the Dodo; it's extinct. The best substitute (with rewired sockets) is the 6GH8, but that type is out of production and supplies are dwindling. AAMOF, all suitable pentode/triode types, like the 6U8 and 6BL8, are headed towards extinction too.I suggest you buy several sets of power section small signal tubes, while it's still possible. A 2 tube set does not have to be "matched", but should come from a single plant and a single production run. Even that low level of selectivity may be difficult to achieve, given the dwindling supply situation.
There is hope, for the time when suitable pentode/triode tubes cease to be available. The excellent EF86 small signal pentode is in production and fits 9 pin mini sockets. OK, the voltage amplifier is taken care of, but the "concertina" phase splitter remains. Adding an additional 9 pin socket to the very limited space is not particularly feasible. However, "sand" rides to the rescue. The ZVN0545A TO92 case MOSFET is space efficient and it makes a nice, highly transparent, DC coupled "concertina" phase splitter.
If you are going to own "vintage" tube equipment, some technical skills are necessary. If you lack such skills and are unwilling to acquire them, you'd better have a very, very, "healthy" bank balance.
edit: fixed "typo"
Eli D.
Edits: 04/20/15
Sovtek used to make an O.K. 7199 equivalent. Is it that this tube is not used in guitar amps?
I like your EF86/ ZVN0545A TO92 case MOSFET solution. Will it drive a pair of 6550's?
Dave
The Russian 7199 "equivalent" is out of production and, as you surmised, New Sensor IS guitar amp oriented.
The EF86/ZVN0545A combo could be OK, with full pentode mode KT88/6550 "finals". I have my doubts about UL mode. As there are several satisfactory replacement driver boards for Dyna MK3s, the issue is (IMO) moot.
JMO, Dyna/Scott/Sherwood style small signal circuitry is at its limit with EL34 class tubes. I definitely prefer Mullard and Williamson style circuitry, when the 6L6 family and KT88s are the "finals".
Like the 12AX7, the EF86 is a wimp that "can't fight its way out of a wet paper bag". The capacitances of the ZVN0545A are tiny and the wimpy types drive the little FET quite easily. I'm not comfortable DC coupling something like an IRFBC20 to the wimpy types.
Eli D.
Yeah, the 7199 issue is definitely a concern with these. I have a stock of 4 strong ones in addition to what I have running in the amp right now. Couldn't hurt to stock up on some equivalents in case I need them. The 6gh8a's look to be plentiful and inexpensive...for now.
I have 4 strong 7199's as well as these nifty little adapters.
There is no need to rewire your amp to accommodate the 6GH8A or 6U8A. Just plug 'em in and play music.
Meat; It's the right thing to do. Romans 14:2
... and while I guess you could say they "worked," the results were FAR from good. Nothing wrong with the new tubes or the adapters that I can find, so it was probably just that use that was inappropriate. I have an S-5000 that is waiting on some transformer work, so I've got time and space to do any rewires, but I may wait and try the adapters before committing to a new tube config. I've been laying up 7199s here and there for a few years, I have 3-4 sets of NOS, but I believe the Sherwood runs them pretty hard, so I'm keeping an eye out for alternatives in case I get tired of shelling out $20+ per tube, like the last set.
you didn't make them yourself? Thanks.
I picked mine up on Ebay.
Just search 7199 adapters.
Meat; It's the right thing to do. Romans 14:2
nt
Very nice! Also have an S-2200, but without the MPX adaptor. I recapped it last year and replaced the dual-concentric volume pot with individual pots. Mine was so corroded that repeated DeOxit treatments couldn't bring it back. All original Sherwood brand tubes in mine!
Before I get scolded for stacking--I'm using two PC fans connected to a wall wart to exhaust hot air from the S-5000's power tube chimney and from the case. The amp stays cool to the touch and the tuner doesn't seem to suffer from any drift.
No MPX adapter = no or very little problem. :> ) DIYer extraordinaire S. Bench has provided us with a nice IC based design. The only potential real trouble is the drive capability of the discriminator and a JFET buffer will dispose of that.
Eli D.
I'm uploading the schematic.
If you are willing to loose the loudness function, buy a hot molded PEC KKA control from DigiKey. Otherwise, try to run down a Noble conductive plastic control, which does have a loudness tap. Carbon sounds better than plastic, unless you buy the OUTRAGEOUSLY expensive P&G stuff.
Time and again, I find myself making the same recommendation for units from this time frame. Tape head I/Ps are passe, in this day and age. Switches in mV. level signal lines are a prescription for trouble. Replace the source selector switch with an approx. $5 Lorlin part from Mouser. Hard wire a pair of I/P jacks to the low level mag. preamp section, which is permanently configured for RIAA. The O/P of the phono section is just another line level source. All the other I/P jacks should be set up for line level signals.
If you plan on recording L/Ps to tape or some sort of digitized version, you really need to go over the low level mag. preamp section. Unfortunately, 12AX7s are wimps that can't drive downstream loads.
BTW, the primitive integrated circuits containing only passive parts, known as PECs, and used in signal shaping circuitry SUCK. Replace them with modern, high precision, discrete, parts.
Oh yeah, the "routine" safety warnings about "death cap." removal and a 3 wire power cable apply.
Eli D.
When my Sherwood S-5000 was rebuilt by Mike Samra, he replaced the old 2 prong power cord with a new 2 prong power cord.
Are you saying Mikey Should have replaced it with a three prong instead of the new two prong?
Meat; It's the right thing to do. Romans 14:2
I don't use a three prong for fear of hum. I use them on a Cit 2 but not on most amps that didn't have them.I use all polarized plugs tho.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Edits: 04/21/15
A polarized plug is an improvement over OEM. Using a DPST switch for the on/off function to completely disconnect from both "legs" of the AC mains, when the unit is not in use, is another step that can be taken. Every little bit helps.
Eli D.
I figured.......You always have a method to your madness.
Glad your recovered.
Meat; It's the right thing to do. Romans 14:2
Ground loop induced hum can occur, when 3 wire, safety grounded, power cables are installed. Do you compromise safety or do you expose yourself to hum? Name your poison. :> (
JMO, on work done for another party, complying with current law, rules, and regulations is the way to go. That means 3 wire, safety grounded power cables. As Jim McShane says, "I'm a chicken". On a "1 off", done strictly for my own use, taking a safety risk is not completely out of the question.
Aside from loop breaking transformers, connecting associated components to the same AC power wall box is a way to get rid of hum.
Eli D.
Just about every 5000 schematic I have seen, I cannot read because the print is so small. If I enlarge it to a readable size it's all fuzzy and unreadable, go figure. So I'm going to share what I have that has worked for me. I got a PDF of the manual some time back and it is the only schematic that I can work from. I do not know how to link it to a post so if anyone is savvy and wants to guide me please do. In lieu of that if you want a copy email me.
Mr Bamboo, thanks for those values, it jogged my memory.
Edits: 04/20/15
Eli,
That's the best scan of the original schematic I've seen yet. I worked off of a SAMS scan when I did my recapping. What I'm looking for is an annotated schematic that people use when they mod these--maybe something like Tronola's Eico ST-70 guide. Maybe nobody's done that for this amp.Anyway, I already took care of the safety caps and put a polarized plug on the unit. I'll check out the suggested tape head mod--I have no use for those plugs as of now and it would be nice to gain an additional set if I wanted to add any more sources. As it is, I've got stuff connnected to phono, AM/FM, aux and TV/MX.
I'm curious about the PECs--they're essentially black boxes to me right now. How do I find out the discrete components I need to swap those with?
Edit: Looks like the SAMS pretty clearly lists the components of the PECs. Do I just swap out identical value components for these?
Edits: 04/19/15
If you would be so kind and share the info SAMS gives on those PECs.
I'm looking to do the same as you.
Here's what I see in the SAMS:K1 (Rumble Filter): Caps: 270mmf, 390 mmf, 470mmf, 6800mmf Resistors: 150K, 1meg, 10meg, 22meg
K2 (Tone Compensation): Caps: 3300mmf, 3300mmf Resistors: 50K, 150K, 470K
K3 (Rumble Filter): Caps: 270mmf, 390mmf, 470mmf, 6800mmf Resistors: 150K, 1meg, 10meg, 22meg
k4 (Tone compensation): Caps: 3300mmf, 3300mmf Resistors: 50K, 150K, 470K
In the SAMS schematic, these are located in dotted line boxes labeled with the K numbers.
Edits: 04/20/15
"
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
That looks like the SAMS that I printed out on the plotter at work before I recapped. Do you keep a marked version that you use for modding? That's the sort of thing I'm interested in seeing. I've seen mention of changing things like the filter cap values around here but haven't seen anything really specific.
Not speaking for Mike but to ask for his mods which is possibly his bread and butter seems a bit insensitive. If you walked into my law or accounting offices and wanted my work product for free, you would find out how hard the door was as you sailed out.
Erslns like Mike spend countless hours and money to find out what works and what does not and I am amazed he offers as much advice for free as he does.
Sorry Mike for speaking out of turn and before consulting with you about this but it hits a nerve with me because of my professions. I actually had to stop going to parties because everyone wanted free advice. The worst were those sho could well afford my fees.
Don Brian Levy, J.D.
Toronto ON Canada
Brian,
I get where you're coming from--my in-laws are doctors and I specifically make it a point to not ask them for medical advice because everybody else in the family calls them as soon as they start feeling ill.My experience over at AK is that most of the people working on the stuff love to talk shop about their mods, and there's never a shortage of people that want a vintage amp without having to work on it. If that's different here, I'm not going to be offended if somebody tells me it's proprietary information. I'm just somebody that will always choose to do the soldering himself if that's an option, because it's half of the fun of this hobby in my opinion.
Edits: 04/21/15
Brian
He didn't ask for my mods but I would give them to anyone.I love to share.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
That's you, Mike!
Dave
I do so many Sherwoods and Macs that I have the mods in my head.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Understood...since I'm not an EE, I tend to restore to stock unless I've got detailed instructions otherwise. That said, my S-5000 sounds great as it is and I've got nothing but respect for the engineers that designed it.
" Looks like the SAMS pretty clearly lists the components of the PECs. Do I just swap out identical value components for these?"
Bingo! You can try mounting the new parts on a small piece of perf. board.
A polarized plug is NOT good enough. Protect your @ss and the folks around you. Put a proper, 3 wire, safety grounded, power cable in.
Eli D.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: