Harman Kardon Prelude 6V6 Schematic

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Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Tue Jun 15, 2010 4:21 pm

Hi All,

New guy here, and although I'm an old guy, I'm just starting out in getting serious with amp maintenance. I know to drain the filter caps, and I want to be able to do recap jobs on my aging amps. My search for a good multimeter has begun, FWIW.

I have a 1957 Harman Kardon PC200 "Prelude" mono hi fi amp. It's been in use in my family since it was acquired as a new unit, first as a hi fi component and then as a guitar amp. It works well, and here's a pic of it in its "native habitat" as I used it this morning (driving a VT 4-12 cab with a Boss FRV-1 reverb pedal in front of it):

Image

The tone has degraded a bit and I think it could stand a recap (and possibly a re-tube). I found a schematic for the PC200 on the Harman site, but it's for a version powered by EL84 tubes. Does anyone know where I might get a schematic online for the 6V6 version?

Alternatively, would the EL84 schematic be sufficiently similar to the one for my version that it would be helpful?

Thank you!

Old Ampeg Guy
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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Wed Jun 16, 2010 2:12 am

There is a book out by Aspen Pittman with a disc in the back with many amplifier brands and models' schematics. I have seen a portion of them on my pc from the disc, but don't have the disc here as it is stored far from my home. I have seen some of his book online. You might try there in Aspen's literature for Harmon Kardon,( I think I spelled that right), good luck and welcome. I just joined yesterday and I can't believe how knowledgable people are on this site. I though I was an enthusiast. This is a great site and a few have infomed me already about the inside of a Princeton Reverb. In two days it sounds better than it has in two years since I bought it. I know just enough to get around. I hope your amp rebuild/recondition goes well. Please let me know what company and details of the tubes you are choosing, I use 6v6 also. Thank you, crowdaddy.
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Re: Harman Kardon Prelude 6V6 Schematic

Postby jaywalker on Wed Jun 16, 2010 4:21 am

here is a thread on audio karma regarding that schematic and just maybe, it being a small world and all, this just might be our own Painterman here on PP. Regardless, it is out there and you could contact them for a copy. Welcome to PP.
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Wed Jun 16, 2010 5:51 pm

crowdaddy wrote:. . . good luck and welcome.


Thanks, crowdaddy! I've read about the Pittman book, but I recently bought Gerald Weber's "All About Vacuum Tube Guitar Amplifiers" and I'm going slowly through that. The basic concepts are great, and may be applicable to something as (relatively) simple as the Harman Kardon, even though it's a hi fi amp rather than a guitar amp. I think the power section will be roughly similar to 6V6 guitar amps and the tone circuitry will be the major difference (e.g., the "Contour" control, the "Roll-off" control, and the "Rumble Filter" on the HK).

. . . This is a great site and a few have infomed me already about the inside of a Princeton Reverb. In two days it sounds better than it has in two years since I bought it. I know just enough to get around. I hope your amp rebuild/recondition goes well. Please let me know what company and details of the tubes you are choosing, I use 6v6 also. Thank you, crowdaddy.


Yes, it's an outstanding site. I never knew about the "Fliptops" Ampeg parts sales site until I arrived here. I'm glad you were able to improve the sound of your Princeton Reverb--that's a nice amp.

As far as the tubes go, I'll probably go with either JJ or NOS tubes (unless someone here tells me there's a genuinely better choice). I'll post when I get there!

I need to find a decent online source for a new Fluke 77 IV multimeter before I tear into the HK.

Thanks again!

OAG
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Wed Jun 16, 2010 5:53 pm

jaywalker wrote:here is a thread on audio karma regarding that schematic and just maybe, it being a small world and all, this just might be our own Painterman here on PP. Regardless, it is out there and you could contact them for a copy. Welcome to PP.


Thank you, jaywalker, both for the link and the welcome!

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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Thu Jun 17, 2010 12:01 pm

I found a tech who will put a bias pot in my Princeton Reverb. He said that way each time I change tubes I won't have to resolder resistors or something of that nature. He also said it may have one (bias pot) if it was already blackfaced. What do you think?
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Thu Jun 17, 2010 10:07 pm

crowdaddy wrote:I found a tech who will put a bias pot in my Princeton Reverb. He said that way each time I change tubes I won't have to resolder resistors or something of that nature. He also said it may have one (bias pot) if it was already blackfaced. What do you think?


Hi crowdaddy,

Being new to amp maintenance, I'm NOT the guy to ask about blackface Princeton Reverbs (everything I know about that amp would fit in a flea's jockstrap!). Or bias pots for that matter. My closest brush with the venerable PR is that I almost bought one in 1968, but opted for a new Ampeg Reverberocket II instead.

Nevertheless, I thought I'd take a looksee in an effort to help out. I understand from my limited reading that Princeton Reverbs of a more recent vintage do require biasing (see, e.g., the following TDPRI thread: http://www.tdpri.com/forum/amp-central-station/40369-do-power-tubes-princeton-reverb-need-biasing.html). Disregarding the fact that the following humorous page assumes the ownership and use of an oscilloscope to perform the bias, some of the info might be helpful to you: http://www.tone-lizard.com/Princeton_bias.htm. This site also appears to concern silver face Princeton Reverbs.

It seems to me that your amp would in fact use resistors to bias the 6V6s. In my brief search, I did not find anything about blackface PRs having bias pots. I'd check with others about that and about this subject in general. I hope those links were helpful. Frankly, this is an area I need to learn myself. My admittedly ignorant view is to let the guy install the pot if he can describe to you a reliable and SAFE way to measure the idle current as you manipulate the pot to achieve an optimum bias, and if you have good reason to believe the guy is reliable and knows what he's doing. I'd like to know what that reliable/SAFE method is (probably something very simple, given that bias pots have been built into the bigger Fender tube amps for years).

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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Sat Jun 19, 2010 12:50 am

OAG,
That was very helpful, unfortunately, my background is one of those that needs repeated readings, and the way I see it is I may have what would be called a fixed bias with an adjustable pot installed when it was blackfaced. However, I remember reading that some amps princeton possibly come with an adjustable tube pot. To balance a set of unbalanced power tubes. So if I hadn't left my disc a few hundred miles away that schematic would probably show if it came with an adjustable tube pot. I know when I looked in the amp it looked like old spagetti and I wasn't hungry. But there was definately a blue plastic looking adjustable pot on it. Again, I can't tell if it was installed after market or when fender made it. The solder looked a little shinier so I think it was put in during Blackfacing. So many mysteries, so little time. Thank you. You have made this interesting. Doug
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Mon Jun 28, 2010 1:29 pm

Hi Doug,

My pleasure! Just curious--did you do anything further with the Princeton yet?

For what it's worth, Sweetwater Sound sells Caig DeOxit. I just got some in a shipment with a few other things. It came in a HOSA display package (I know HOSA as the guitar/PA cable people) but the can is definitely DeOxit. I mention that in case you do any work on the amp yourself. DeOxit is great for cleaning out pots and taking oxidation off of contacts.

Jon
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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Sat Jul 03, 2010 10:34 pm

Hey John,
I called a circuit shop, talked to a tech, he recommended Eminece Beta 10 for a speaker and I don' think he had any. He wasn't all that helpful, and wanted to know when I finally have it fixed up as he has many asking about smaller speakers right now. He is mostly hi fi. I'm going to stop by some time but I'm getting ready to travel. The contact cleaner I found around the house is called carbontetrochloride I think and I used it so many years ago I don't know if it should be used or not so I'll look for deox, the right stuff. I've played my amp quite a bit lately and have enjoyed switching tubes for now. I put an Ei in valve one and am ordeing a jj for it and some jj 6v6. I would like to try rca in valve one. Also I flipped it over to check for the possibility of a 12 inch but my little g-10L35 sounds good with the tube switch. I have considered a bunch of different speakers, I tend to move slower these days. The jbl e110 or k110 is sounding better and better as the bass response on a 10 inch is sub par with most 10 inchers. I like this project because of the nice sounds I'm getting. Another tech from my area, who has a good reputation, I actually think he went though my amp before I bought it, told me with the princeton, the tubes and speakers are all I really need to change for some good tone. I have decided I like clean soundeing amps. Some dirt with a triple xxx is available to me for some rock if need be. How is your project coming? I have seen some interesting harman Karden amps on ebay lately. What type of cabinet and speaker are you going to run? Have a great 4th
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Re: Harman Kardon Prelude 6V6 Schematic

Postby PeterS on Sun Jul 04, 2010 8:48 pm

he recommended Eminece Beta 10 for a speaker and I don' think he had any. He wasn't all that helpful, and wanted to know when I finally have it fixed up as he has many asking about smaller speakers right now. He is mostly hi fi.


Eminence Beta 10 for a Princeton is probably a choice only a hifi guy would make. Post in the Fender section and you'll get some other opinions, there's lots of good 10" speakers.
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Mon Jul 05, 2010 10:55 pm

crowdaddy wrote:Hey John,
I called a circuit shop, talked to a tech, he recommended Eminece Beta 10 for a speaker and I don' think he had any. . . . The jbl e110 or k110 is sounding better and better as the bass response on a 10 inch is sub par with most 10 inchers. I like this project because of the nice sounds I'm getting. Another tech from my area, who has a good reputation, I actually think he went though my amp before I bought it, told me with the princeton, the tubes and speakers are all I really need to change for some good tone. I have decided I like clean soundeing amps. Some dirt with a triple xxx is available to me for some rock if need be. How is your project coming? I have seen some interesting harman Karden amps on ebay lately. What type of cabinet and speaker are you going to run? Have a great 4th



Hi Doug,

I am a huge fan of JBL guitar speakers. It's too bad they don't make speakers specifically for guitar and bass guitar any longer (all of their commercial drivers appear to be for P.A. use). I would go with the E110, and possibly the K110. I don't know much about the K series, but the E series is a successor to the famous "D" family. I have a D120-F in my late 1980s Fender Studio 85 solid-state amp (I think of it as my "sort of" Polytone--it's for my efforts to play jazz). It's clean right up to thunderous levels, which I like. I agree with you about clean sounding amps.

Given that a JBL guitar speaker will be a used one and fairly old (unless you can find a New-Old Stock one), you might be looking at having it reconed. I went through that with my D120-F. Maybe you can find one recently reconed.

There are some very good alternatives out there, though. Look at Eminence speakers, for example. Their offerings are kind of limited when it comes to ten-inch speakers. Can you shoehorn a twelve-inch into the cabinet? I cannot recall the dimensions of the Princeton. If you can, look at the "Swamp Thang" twelve-inch by Eminence. It has very good sensitivity, and might give your Princeton a very big "voice."

Here's a link to a TDPRI forum thread about twelve-inch speakers in Princetons: http://www.tdpri.com/forum/amp-central-station/158528-who-put-12-speaker-there-princeton-reverb.html.

I have not yet started on the Harman Kardon. We had some huge veterinary bills for my cat, which unfortunately we had to euthanize after he was in the emergency hospital for four days. I was going to buy a multi-meter (a Fluke 77 IV), but since I want to buy a new one, I'm holding off a bit until my "guitar/amp" fund gets a bit replenished.

I run my guitar into the Harman Kardon through a Boss FRV-1 pedal that is intended to replicate the 1963 Fender outboard reverb unit. From the Harman Kardon output, I've been running it into a VT four-twelve cabinet (VT is Vibration Technology, a Canadian company that apparently no longer makes guitar amps). I bought that cabinet back in 1980. It has four Celestions, but I haven't had the speakers out in many years so I cannot recall exactly what they are. I'm going to pull one soon and look.

With the Harman Kardon, even with its elderly tubes and caps, the cabinet is quite loud. It's even louder with my Reverberocket 2, which I converted to a head back in the early 1970s.

Yes, there are a couple of decent-looking Harman Kardons on Ebay: the Trend amp (which I think is stated not to be producing sound) and the Prelude II. I've been tempted to bid, but can't do it right now. I'll see how things go with my own Prelude. It should sound fairly good once it has had a good refurbishing (assuming I can accomplish that!).

Thank you for the 4th wishes! I had a good one, and I hope that you did, too!

Jon
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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Tue Jul 06, 2010 8:36 pm

Jon,
Its tough to loose a best friend no matter, big or small, human or pet. Sorry to hear of it and hope that your loss is remembered, as I'm sure it is, of all the good times. It was good to hear from you, and I'm glad you told me, I know something about loosing a best friend. Your project sounds like it is one that is making use of a boss reverb. I like boss, and have at least one pedal, the harmonizer, I only use it now and then for octives and I've found that it can strengthen a guitar signal somehow. Makes it fatter if thats what your after. As for reverb I can't do without it. Just makes it livelier. Your cabinet sounds monstrous, but thats always good. Do you trade off then with the rebult reverberocket head and the harmon? When I make it to my destination later in the week, I'll look on my disc, and then maybe you can tell me how to load and send it to you if it has H/K? Yes, it seems like the jbl may have a home if I can find one. I haven't ruled out any of them, I'm sorta holding off on the 12 inch idea, because if a 10 works, for what I'm doing I could avoid the cutting. I put my princeton in front of a mic on a recorder/jamman, to put song ideas on. The volume is at 2 for that so, until my guitar fund comes up a little, I'm going to rearrange cables, its cheaper. Keep me posted if you can. Doug
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Re: Harman Kardon Prelude 6V6 Schematic

Postby Old Ampeg Guy on Sat Jul 10, 2010 1:53 am

Thank you for the kind words about my cat, Doug. He was a great little guy and we're still in mourning. We did get another cat from the pound, a large black Domestic Long Hair/Maine Coon mix, which my wife suggested we name "Les Paul." So we did. :)

I'm kind of leery of pedals these days. I have a few from my hard rock days. I still play rock, but I'm striving for more of a neck pickup jazz tone, so I pretty much go straight into the amp.

Like you, though, I really like reverb. That's why I broke down and got the Boss FRV-1. I really couldn't afford one of the actual Fender tube reverb units (the outboard ones that were used in the 1960s and have recently been reissued by Fender). The FRV-1 does a decent job of providing just that jazzy Fender touch of reverb once you turn all the knobs down then back up again slightly.

I'd be interested to know what you decide as far as the speaker goes for the Princeton Reverb. If you have a second baffle made, you can keep the original one with the ten-inch speaker and put a twelve-inch speaker in the new baffle, and just mount that one in place of the original.

Right now I'm running the Ampeg Reverberocket 2 into the Fender twelve-inch speaker that came with my Fender Studio 85 and which is now mounted in a square box that's about sixteen inches on each side. I also use that speaker with my Carvin ProBass 150 head (I don't turn that up very much).

It's only the Harmon Kardon that is plugged into the VT four-twelve cabinet right now. I'm wondering about the Harmon Kardon--it's 53 years old, but it's very quiet. I can't imagine caps normally last that long, but perhaps the power supply caps at least are still reasonably within spec. I guess I'll know once I get that multi-meter and open it up!

I like the sound of your recording setup. I need to have something handy here at my music computer desk that I can put ideas on, like you have. I have the software, but I have to do a shutdown/restart with my Firewire audio interface. It would be nice to get something I can just turn on quickly like your Jamman to capture music ideas.

Jon
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Re: Harman Kardon Prelude 6V6 Schematic

Postby crowdaddy on Wed Jul 28, 2010 5:59 pm

Jon,
Well it isn't much and the loop cycle is throwing me off and I can't find the manual. I think you can switch from loop to single for longer recording but I need to look around for the manual. I've been traveling some, and at night studying the schematics to super reverb and princeton reverb, ect. and I didn't see any Harmon Kardon schematics on the disc. sorry. Have you found a schematic to your amplifier? I tried some different tubes because I think I told you I have these non expiring gift certificates from a wonderful music store. They have to be spent some time. So the little amp got some more power and a litlle warmer sound to it. Anyway let me know what's going on your way when you can.
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