US MADE
1992
This is my first real guitar amp. It is a very nice 2-channel all-tube amp inspired by the VOX AC30.
It is equipped with 3 x 12ax7 and 4 x EL84 vacuum tubes and has an output rated at 50W. This amp has 2 x 10" 50W each ceramic Eminence speakers. It has a long-pan spring reverb with solid-state driver and recovery stages.
It has an effects loop and footswitch channel switching. An additional capabilty that is unique to this model is the quadra-verb channel and boost switch capability using an optional 4-button programmable footswitch.
I love the clean channel of this amp. At a specific setting recommended in the manual it has a fat and smooth overdriven sound. A Les Paul type guitar can drive this amp into a very nice overdriven sound without using any outboard effects. This amp is also pedal-friendly and it is very easy to get nice singing distortion sound using outboard effects.
Though marketed as a 2-channel amp, I view this amp as a very nice one-channel amp (clean channel) with a fooswitchable cascaded overdrive stage. The first 12AX7 is the preamp, the second 12AX7 is the OD cascade stage. The 3rd 12AX7 is the Phase Inverter tube.
The internal construction is excellent and techies would be happy working on this amp.
It has one well-laid out thick double-sided pcb with most parts on it easily accessible. All wiring connections to the pcb (except one, the on/off switch connection) has push-type connectors and the pcb could be easily taken out completely for servicing. With regards to this issue, this amp is considerably better than even my Fender amps, vintage and pcb reissues and much better than similar VOX inspired amps like the Peavey Classic 30/50 and Delta Blues.
The 4 power tubes are directly installed in the chassis, only the 3 pre-amp tubes are installed in the pcb. The above Peavey amps have their preamp and power tubes directly mounted on the pcb. Considering all the heat the 4 power tubes generate while the amp is "ON", this is another important advantage.
This particular amp model was purportedly designed by Randall Smith of Mesa Engineering for Seymour Duncan. This would explain why the original power tubes in the Seymour Duncan 8450 is a quad of Mesa Engg branded tubes (as also stated in the manual).
Amp Manual
40 comments:
I own one of these... I searched the web for reviews This is the most informative so far. I love the sound And I think If it last I will hang to it.
hi Nuno, thanks for your comment! With normal use and maintenance, these amps should last a long, long time...Cheers! Romy
I would like to buy one. I play mainly in clean mode, jazz and blues type music, I need overdive only for some blues settings. Can you tell me something more about clean sound and humbucker of the hollow body guitar? Thank you! :-)
I bought an 84-50 head for $500 in Melbourne, Australia. So far, it's treated me well, and seems to retain good definition with high gain.
I would love to know if Randall Smith had anything to do with its design.
@Zoran, if you get an opportunity to buy one at a good price, i suggest you go for it. The amp is quite similar soundwise to the Peavey amps, the Classic 30, the Classic 50 and the Delta Blues. Thank you for dropping by! best regards, romy.
@computerthomas, congrats on your new old amp! I read about the Randall Smith connection to the design of the amp from a review in the internet. The use of Mesa Engg power tube complement convinced me of this. The elaborate Quadraverb switching is another hint to this connection in my opinion. thats my take on this unless somebody will show otherwise...enjoy and thanks for dropping by! best regards, romy
@sd8450 Thank you, I got my SD 8450, about one month ago, and have to tell you were right. The sound is lovely, especially the clean channel, but the OD is also fine. I've bought mine for about 430 euros used (changed my Peavey Bandit 112 and paid extra 100 euros). It has some modifications, the additional stand by switch, and Eminence Red Coat Wizard speaker. It's one of the last amps, the production date is December 1992. Sometimes I have a hum that comes and goes without any noticeable regularity, I'll have to have it checked by some good tech. Thank you once again and keep on picking! Cheers, Zoran
how much did the amp cost you?
hi ben2595,
i bought the amp in 2004 from a used music store in Hanoi when I was there for a job. I am sorry but I could not recall the purchase amount. I still have the receipt in my house but I am on an off-shore assignment at the moment. It may have cost me around USD500 or so including the shipping to Manila. thanks for dropping by! romy
Hello,
Do you have the footswitch for this amp. If you do I would love some photos of the inside of the switch. If not how about a photo of the footswitch connector on the inside of the amp. Any help would be greatly appreciated.
Hello,
I have been using one since early 90´s. tubes have been changed couple of times but othervise it has been my trusted workhorse.
I use it with closed cabinet with 4x12" celestion greenbacks from the 80´s.
I like the sound of the real tube overdrive. I used to have a tube screamer but traded it away. Why should one use a stompbox to imitate real tube overdrive when you can get a real one from your amp? I think its value is much more than what you get from it today. I´ll keep this amp even I would buy another one.
Jyrki,
Helsinki, Finland
EUROPE
Hi Unknown,
I meant to answer earlier regarding the footswitch question. I don't have the footswitch and it is quite rare.
I do have a clear schematic of the footswitch and the amp itself which I meant to post. I however have only a free Photobucket account and this only allows pictures to be uploaded. Photobucket requires a paid subscription to be able to upload other documents like PDF etc. These have to wait until I can find a solution...
Hi AlGee / Jyrki,
Thanks for dropping by and chiming in!
The amp has stayed under the radar and is relatively undervalued for being a USA-made amp from a well-known personality in the business.
We know better so good for us!
Cheers! Romy
@Romy If you could send the footswitch and amp schematic by email, that would be more than great! :-) If you can do it, please inform me or simply send on my email: drdukic@gmail.com. I've tried hard to find it somewhere on the web, but there was no reliable source. Cheers, Zoran
have you modded this amp in any way ? i see some different components than the 8450 i own ?
@Zoran,
You can now download the schematics from my latest post 'Schematics'. Cheers! Romy
@fisher gary,
I believe there were 2 components replaced by the previous owner of my amp. One is the resistor you can see at the upper-left corner in the circuit board (brown and no markings) and the big capacitor close to the output transformer at the lower-right of the circuit board. I would be interested to see a picture of your amp to compare. If you got the time please send to rrcmail2003@yahoo.com. Thanks for dropping by! Cheers! Romy
yah i had to replace my 7.5 ohm resistor in the left corner when i got the amp, thats the brown one you are pointing out. bugger cause nobody on the earth seems to have that value 7.5 ohm 2w . i was curious about the big capacitor because i believe the one your using is 450v something ? uf (maybe you could fill me in )can't quite read the other bit. mine only has a rating of 350v something uf . was wondering if it effects the sound ? anyways i'll try and get some pics for you soon.
i also think your resistor r64 has been swapped for a metal oxide resistor .. the one i have is an old ceramic beige one.
@fisher gary,
I've seen your email and the attached pictures. Thanks!
It appears that the previous owner of my amp tried to improve the amp by replacing both R64 and C39. The resistor (R64) appears to me to be a voltage divider and C39 serves as power filter capacitor supplying 335V to the preamp and tone control stages of the amp. Metal film type resistor is known to be less noisy than carbon film or carbon composition resistors. The bigger cap 47uF 450V provides more smoothing of the rectified power and 450V Working Voltage provides a greater safety margin vs. the original capacitor (33uF 350V). The supply voltage is 335V so there is just enough margin with a Working Voltage of 350V. The original cap which your amp still have is perfectly fine and it is up to you if you think it is worth it to change to the next higher value.
If you still want to change that R56 resistor to a more correct value, I suggest you consider a wirewound resistor (the rectangular white ceramic type). You can get it at the correct resistance (7.5 ohms) and its okay to get 2W or the next bigger size if 2W is not available). Mount it a bit elevated from the circuit board for heat dissipation. i hope this helps. Cheers, Romy
hi i have a question for any of the seymour duncan 8450 owners- does any one know the number of the reverb tank thats in it... by this i mean the accutronics # something like 4beb31b - a number like that ?? i think my tank is going but i have no idea what reverb tank it is - any help would be appreciated ..
sorry for asking , i just found the answer on the net... its a accutronics 4BC3C1B tank. thanks anyway
hi was wondering the value of R42 in the 8450 amp if any one could tell me. the schematic is far too small to read on my computer ... or if anyone could send me a version of the schematic.. i think it is 100 ohms but i am not 100% sure.. i wired this amp to my speakers at 2 ohms ... everything survived except i think i wore my tubes a little and blew this resistor went out of spec.. very strong amp this one ..
i have the4 footswitch which is awesome - it has 4 switches and each one is adjustable in 4 or 5 ways. really allows you to fine tune the amp with the touch of a button . if
you would like a picture of it or inside it please email me. i will try and find it.
Hi All,
I need some help with my SD 84-50 and came across this blog. So I wondered if anyone could help?
I bought my amp 2nd hand around 1996/7. I absolutely love my amp and basically saw me using it for the indefinite future until recently. I was at the rehearsal studio for 4 hours then right on the last song my primary fuse blew. I thought no problem I'll change it when I get home. But to my horror it kept blowing the new fuses.
I downloaded the schematic for this amp but to be honest its too blurry to read (anyone have a better copy?) I did notice my R56 (750 ohm 2W) & R58 (1K 2W) had burnt. So I replaced them thinking that they may be the problem, but my fuse kept blowing. So I took my amp to a amp repair man, he had a quick look, my output valves where not shorting what he first thought, he then went on to tell me it would cost more than the amp was worth to repair but he did indicate my output transformer could have gone. I checked my output transformer when I got home with some basic tests. I checked the resistance on the primary side, the B+ to the other two wires going to the output valves one side read (brown wire) 3.1K, ( blue wire) 175 ohm's. Could anyone tell me if this is normal or has my transformer fused?
If this is the case,
1, what transformer could I replace it with or what would I be looking out for ? I have seen the hammond transformer but didn't know what I needed, someone used the the 'hammond 1650f' on their 84-40.
2, what was have caused my transformer to brake?
Sorry for a long winded write up, but any help would be very appriciated.
you know if you email seymour duncan they can send you the schematic . just explain yourself a little thats what i did . i don't have it now or i would send it to you .
Hi Mark Noe,
Let me have your email so I can send you the schematic.
1. Replacement output transformers for the Peavey C30 or Peavey Delta Blues 210 which also uses 4 x EL84 output tubes would do. The only problem is that these might not fit inside the chassis of your amp and you might need to have it installed at the bottom of the chassis. The original output transformer is quite small in size. 2. One possible cause is if there is a break of the wiring to the speaker, (equivalent to having no speaker connected to the output side of the transformer while the amp is in use). Try measuring the resistances of the OT windings including the secondary side but this time disconnect all the leads of the OT from the circuit just to make sure the OT is really busted before buying a replacement.
please send me a schematic as well ...fishergary539@gmail.com
Hi Romy,
Thank you for your help and reply. My email address is mark.noe@btinternet.com for the schematic.
I have totally discontected my OT and still getting 3.2k & 176 ohm on the primary side. Im also getting continuity from the primary to the secondary.
Before I disconected my OT, I just removed the B+(plate) wire and my amp turned on without blowing a fuse and all 4 EL84 glowed.
Is this sure thing that my OT is bad?
would this output transformer work ?
http://www.valvewizard.co.uk/OT.html
This one seems quite cheap, that would suit my pocket as a cheap replacement.
Hi Mark Noe,
The schematic is sent to your email.
Your test confirmed that the OT is busted.
Hope you can get the amp running very soon!
Best regards, romy
Hello my friends could anyone sendme the sd8450 footswitch schematics? Thank you.by the way i love this amp.funkysoulbrother@gmail.com
Hey guys...its me again.please can you send me the seymour duncan quadratone footswitch schematics? Pleaseeeeee... funkysoulbrother@gmail.com
hi ... i have a working quadratone footswitch if anyone is interested .
Hello, I have this amp in head version with a dead power transformer.
In the schematics I can figure out that the firt secondary is 12V-CT, but can't figure out the second secondary voltage wich creates the 550VDC via a doubler. This should be around 300VAC ?
Could you measure it in your amp and tell me ?
Hello i just bought one of these at a auction along with alot of other treausures from the 60s 70s and 80s if interrested in buying ill sell for 500 firm let me know 9418222438
Howdy all. I have 2 of these amps, guess I like em! I've had issues with them though. One thing I and others seem to have experienced/reported is either drop out, or intermittent distortion (not from OD channel). At first it sounded as if it may have been caused by poor contacts in the input jacks and/or effect send/return. I gave them a good clean but no luck. I noted my R58 was heavily burned and thought it could be the culprit. Replaced it, still no cigar.
I then started to take a look at whether there was a larger grounding issue and noted something others might find useful. As far as can tell, the PCB is grounded in what I think (and now know) is a slightly unreliable way. The grounding is via a single one of the PCB mounting posts. You can see some exposed PCB track around one of the screws, thats the one. What had happened with both my amps is that the screw, over time has become slightly loose meaning that with either a bump or vibration from the speaker when playing, the PCB became ungrounded. By simply tightening the screws up, the problem vanished entirely. To test, I also remove the screw thus ungrounding(is that a word?)and the problem came straight back.
Bonjour .je viens de trouver une annonce d un ampli SD84 50 qui aurait été fabriqué pour rickenbacker. L un de vous si cela est possible ? Merci
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