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Post subject: Packard Bell Model SA-5 Question
Posted: Mon Sep 16, 2013 4:52 pm
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I have a Packard Bell Model SA-5 tube amp that i have been messing around with ..I have it so i can play my guitar through it but it needs a tone stack and I am also wondering if any knows if it was set up for hi fi? it sounds really clean (probably the 12au7a tube) if i posted a picture could someone tell me if there is something that needs to be removed to make it sound better for guitar? this was an amp for having a external speaker for your record player back in the old days. Its really cool I was hoping for something like a champ type thing i believe it is 5 watts. thanks JL


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Mon Sep 16, 2013 5:39 pm
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If this amp is for a movie projector --- most are single-ended or simple push-pull 6V6GT amps. Photos would definitely help. Either case, the circuit is prolly clsoe to a Champ (SE) or Princeton (PP).


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Mon Sep 16, 2013 7:27 pm
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it was from a speaker box that was used for a extension spk for a phonograph player i think? I have been using it with my roland micro amp -line out to input on tube amp,,sounds good too.. i will post some pix


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Sep 17, 2013 6:34 pm
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[url][URL=http://s1302.photobucket.com/user/jimleach/media/DSCN1116_zpsf1200d60.jpg.html]Image[/url][/url]


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Sep 17, 2013 6:36 pm
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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Sep 17, 2013 6:41 pm
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here are some pictures..any ideas? i tried it with a 12ax7 and it started to make the speaker vibrate really hard? thanks for any help..J


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Sep 17, 2013 8:27 pm
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What kind of tubes does this amp have? It looks like the original output tube was a 6AQ5, so it isn't made for a 12xx7 type tube. The smaller tubes, look like 7 pins. It also appears that the output transformer is made to drive a speaker with a transformer on it.

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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 12:11 pm
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HERE IS A SCHEMATIC I MADE UP. CAN ANYONE TELL ME THE BEST PLACE TO ADD A TONE STACK? I MADE A MARSHALL TYPE TONE STACK AND AM TRYING TO DECIDE WHERE TO ADD IT IN. ANY IDEAS?


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 2:45 pm
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jimitrader,

There seems to be a few things missing or wrong in that layout. There is no main filter caps off the 6X4, which has much too many connections for a rectifier. There are no coupling caps between the 12AU7 and the 6AQ5. And what is "T" in the center of the amp? It can't be a ground points --- as there are too many connections for the three tubes you show. Where is the output tranny?

The on-off switch would prolly not go to the 12AU7. The input is prolly not going to the switch. And where does the speakers (output) connect? Do you have a schematic of the amp? Something that looks like this?

Thanks! :D



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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 2:58 pm
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The T is the big transformer that is up on top by the tubes..I cant find any info on this amp. it was a record player extension amp it sounds ok just wish it had tone control..i looked around and found an article describing how to convert old tube amps for guitar and in the article he talks about this type amp and says its really easy to mod these for guitar..i am still so new at this i am not sure what to do...he talks about removing the feedback loop?

here is some parts of the article:
"
Also very valuable are small tube amps built into remote speaker cabinets that plug into tape recorders or record players, so people out next to the swimming pool can hear your records and tapes too. Look for these self-powered "satellite speakers" from Voice of Music ("VM"), Sears Silvertone, Ampex, Webcor and others. They are the easiest of all to convert, and in addition you get a cheap little loudspeaker included in the deal.


"THINGS TO GET RID OF…
Identification and removal of feedback circuits. Organ and hi-fi amps almost always have a feedback circuit that is used to cancel unwanted distortion. For example, below I have reproduced a schematic for a hi-fi power amp that has a feedback loop running from the 16 ohm tap of the output transformer secondary to the cathode circuit (pin #9) of the 6AN8 preamp tube. Clip it out at both ends and throw it straight into the trash. We are not after hi-fi here- we WANT the distortion!


"Adding tone and volume controls. The tweed Fender Deluxe tone and volume circuit works really well and is extremely simple to build. Below I have sketched it out, inserted between the first and second stage tube sections of a typical tube preamp where the existing tone control and volume knob have been clipped out. The output of the first tube stage is picked off its plate using the 0.02 uF coupling capacitor which leads to the “top” of the volume control pot. Also connected to the top of the volume pot is a line going to the tone circuit. When the tone knob is turned up, the pot wiper points to the 500pF capacitor. This capacitor leapfrogs all the high frequencies over the top of the volume control and sends them straight into the input grid of the next tube. This yields lots of treble. When the tone knob is turned all the way down, the wiper instead points to the much larger 0.047uF capacitor which short-circuits all the high frequencies present on the input grid of the second tube straight to ground. This makes the tone really bassy.


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 3:02 pm
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speakers connect at top left


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 3:10 pm
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This should be the schematic for your amp, kind of hard to read, but it is all that I could find. Keep in mind that the amp could have been modified at some point, and if so, it might not match the amp exactly.

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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 3:18 pm
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I was just looking on that same site.. :lol: yeah its hard to see what it says...thanks though!..I will keep staring at it and dreaming about putting that tone stack in there..do you see anything that needs to be removed? for better sound? does it look like it is ultra-linear like a hi-fi amp?


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Tue Nov 19, 2013 6:28 pm
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jimitrader,

Looking at your photos --- looks like the 6X4 in located where you have the 6AQ5 on the drawing and vice versa.

The output tranny is on the left. The main filter cap in the four connections on the right, right next to the 6X4. The giveaway is the twisted red wires going to the 6X4 (lower-right). The "T" is the power tranny.

Anyhow, better to see a schematic before checking for potential modification. But, I think good tubes and an EQ pedal would do the trick.


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Post subject: Re: Packard Bell Model SA-5 Question
Posted: Wed Nov 20, 2013 11:09 am
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You may want to consider this... the BF Champ (AA764) has a tone stack, while the tweed (5F1) doesn't. Many ppl consider the tweed the tone to shoot for in this single-ended amp. Maybe due to the lack of the second 12AX7 phase inverter stage missing in the single-ended amp. There is less overall gain in the Champ's gain stages, as compared to a push-pull Princeton (AA964).

Your Packard Bell has only the one duo-triode 12AU7 input and gain stage. The 12AU7 already has less mu than the 12AX7. So, I suspect even less gain to drive a tone stack, then the final output. Do you have access to a pedal EQ? Maybe using the pedal's gain stage, you will maintain the amp's proper OD character --- yet still be able to shape the tone.

Anyhow, the BF Champ places the tone stack between the two halves of the 12AX7 (V1). This maybe a good place to start (between the two halves of your 12AU7), then use the Duncan Tone Stack calculator to fine tune the roll-off and overlap of EQ.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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