Author Topic: Spectrum I  (Read 5901 times)

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Anonymous

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Spectrum I
« on: December 12, 2005, 05:53:28 pm »
I have had this amp for some time.. it has sat in storage for about 7 years now.. I have decieded that after not playing for seven years that I want to restore this amp.. doing most of the work my self.. so I am glad that I have found this site.. maybe I will be able to get a lot of answers to what I am sure.. will be many questions.. First off.. I see that there are not any schematics for this amp.. I am not sure.. but the Spectrum II and the Spectrum I.. do not really seem to be the same in a lot of ways.. from what I understand.. The I model.. was to use 6CA7 EL-34's.. and the II was set up for KT-88's.. also.. what is supposed to be the rated output rating for the Spectrum I.. something like 60 watts ?  I am new to restoring this amp.. meaning I have never done anything like this.. so I will go slow.. but I will make sure it is right.. that is for sure.. but I do want to use the best tubes and caps that I can get to get beauty working at it's best..when I am done.. even the chassy will be like new.. clean..making sure.. that the screws to the output transformers are even clean.. having not had it apart yet. i presume that the transformers are grounded to the chassy via the screws that hold them in place? .. So.. what I am getting too.. I know is going to be a chore of love.. I have owned an older non black face coliseum and concert amp.. sorry that I let them get out my hands.. (see what marriage does to you).. so mentoring will be asked for from time to time with this project.. hope you all don't mind me screaming for help.. !  There is a place that rechromes here where i live so i will even get the orginal corner protectors back to looking new.. I know that making it all new my not keep the value up.. but then.. I am not letting this amp get out of my hands.. and it will become a amp that I will use often..

I need to know.. what caps to buy.. which would be best.. I have found some new "fat boy" sylvania EL-34's for sale.. and some RCA's
would you reconmend a Mullard GZ-34 ? Any suggestions would be greatly appreciated to get this nice amp back to being a show amp.. also.. I need to know.. what was the speaker ohm load for this amp.. 4? I am going to build my cabs.. using Eminence Kappa 15's and WinISD program to help design the cab..

Doc

Offline FroggyOne2

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Spectrum I
« Reply #1 on: December 12, 2005, 05:55:18 pm »
The user says guest.. it is really me.. sorry..

Doc

Offline FroggyOne2

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Spectrum I
« Reply #2 on: December 12, 2005, 06:42:58 pm »
ok.. another question.. what is the 1/4 inch plug between the power tubes for?

Doc

Offline FroggyOne2

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Spectrum I
« Reply #3 on: December 12, 2005, 07:17:37 pm »
never mind.. i know what it is now.. it is i think.. is it the adjustable bias pot?

Doc

Offline AdmiralB

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Spectrum I
« Reply #4 on: December 12, 2005, 07:52:17 pm »
Output is in the neighborhood of 40W.  

For cost effectivity, I would recommend JJ E34Ls - or maybe the new KT77, if you can get them - and also their GZ34.

For caps, you can get an exact replacement from Antique Electronics.  I prefer NOT to use a 4-section, myself.  For the first bank, I use two 60uF/350V Sprague Atoms in series, each bypassed by a 220K/1W resistor.  I use a Sprague Atom 20uF/600V for the second bank, then I replace the can with a dual 32uF/500V LCR-style can - I use F&T or JJ, depending upon what I have.

Offline FroggyOne2

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Spectrum I
« Reply #5 on: December 12, 2005, 07:55:38 pm »
ok.. took the chassy out.. before removing the chassy.. took the tubes out.. noticed that the power tubes in the amp were 5881's.. not EL-34's (6CA7)  there have been some mods done here.. but with out the correct schematic.. it is hard to tell what exactly has been done.. i do see that another capacitor has been added between the transformer that is mounted on the chassy (same side as the power switches are) the capacitor is connected between the transformer and the standby switch.. then there is a small resistor looking thing that i can not tell what it is.. that is soldered in between the PBS cap one of the leads to the same transformer.. the wires on this resistor like thing is darkend like it has had a lot of heat on it.. it is marked 2071 over Sylvania and the on the side of the name Sylvania.. 543.  anyone got any ideas what is going on here?

Doc

Offline FroggyOne2

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Spectrum I
« Reply #6 on: December 12, 2005, 08:00:56 pm »
Adm.. thank you for your reply.. wasn't sure what the output power would be on this amp.. after getting into the amp and seeing that someone has been playin with it.. wonder if they have gotten it hot rodded a little too much.. I know that the last time i had the amp on.. seven years ago.. it was clean sounding.. but that is all i remember about it then.. when i looked at the power tubes.. it had a pair of Sovtek 5881 tubes in it..

Doc

Offline AdmiralB

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Spectrum I
« Reply #7 on: December 12, 2005, 08:08:04 pm »
The component you are trying to identify is probably the diode in the bias supply.  There should be two 50uF/150V caps in this circuit, one by the diode, the other over next to the driver tube (7199 for your amp I think).

Yours probably had Sovtek 5881s in it because for a long time they were the only affordable tubes that could take the voltage your amp generates.  Things are better now!

Offline FroggyOne2

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Spectrum I
« Reply #8 on: December 12, 2005, 08:22:33 pm »
ok.. it also has a Dynaco 7043 in it.. the output transformer is a Dynaco A470 and the other Transformer in it has no name but is marked PA135

Doc

Offline FroggyOne2

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Spectrum I
« Reply #9 on: December 12, 2005, 08:28:09 pm »
yes.. there are two caps in that are alike.. both are yellow and are marked "AEROVOX  E26B638 TYPE PRS 50 MFD 150 DCWV 6704"

I was thinking it may have been a diode..but wasn't sure.. being that i am not a electrik  wizord!

Doc

Offline FroggyOne2

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Spectrum I
« Reply #10 on: December 12, 2005, 09:05:46 pm »
let me ask this.. were there two different versions of the Spectrum I.. one with a presence knob  and one without?

Doc

Offline AdmiralB

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Spectrum I
« Reply #11 on: December 13, 2005, 09:06:12 am »
I'm not aware of any tube amps from Sunn with presence until the Model T.

Offline FroggyOne2

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Spectrum I
« Reply #12 on: December 13, 2005, 04:02:06 pm »
Right.. well I did miss type that.. it is a contour knob.. but I have learned a few things in the past 24 hours.. there were two versions of the Spectrum I.. one 60 watt model and which used a 6an8 and the 40 watt which used a 7199 tube.(this information was provided to me by Bob at Eurotubes) .(It is my understanding if I am correct, and please correct me anyone) the 60 watt model is the one with the contour knob on the amp..  the 33uF450v cap that is between chassy ground and the standby switch is a feedback shunt to protect the power output transformer from feedback surges..

Now if this amp that I have is the 60 watt version.. then it came with KT88s.. would this be the reason that when I bought the amp.. it had the 5881's in the amp.. with the re-wire mod from the PA135 transformer to the  Dyanco 7043 ?  Was this done to give more output or to change the tone of the amp?

Doc

Offline AdmiralB

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Spectrum I
« Reply #13 on: December 13, 2005, 04:25:54 pm »
Spectrum I is the 40W 2xEL34 model.  That's what you have, and your transformer codes bear it out.

Spectrum II is the 60W 2xKT88 or 6550 model.

The cap you refer to is a filter, it reduces ripple in the power supply.  It has nothing to do with feedback.  

I would recommend you get some expert/professional help with the project.  Based upon your comments thus far, I'm a little concerned for your safety.  High voltage is terribly unforgiving, and these amps have a lot of it.