Eastern Amplifier 6V6, 6LS7, 6X5 potential

[SIG]

I picked up this Eastern Amplifier, which I believe has a lot of potential. I recapped her and put a grounded 3 prong cord, and she sounds good; however, the preamp tonestack circuit is really noisy and strange to me. Appreciate any ideas for a rewire. Removing the 6LS7, eliminates the noise by the way, and it's a good NOS National Tube. Attaching a schematic I was able to pickup off internet. Thanks for your ideas!

On the front of the chassis the amp says:
 
Eastern Amplifier
Licensed under U.S. Patents of American Telephone and Telegraph Company and Western Electric Company incorporated (see label inside). 
 
Model G1A
Serial NO: 6597

[HotBluePlates]

... the preamp tonestack circuit is really noisy and strange to me. ...

According to your schematic, there is no tonestack in the preamp. It's attached to the output tube plate.

... Removing the 6LS7, eliminates the noise by the way ...

Note that the 6SL7 is the only preamp tube. Removing it then kills anything prior to the output tube, and you should expect that to remove all noise.

... Appreciate any ideas for a rewire. ...

Here we go!

The volume pot is in the wrong place on this amp. It is fed from the input jacks. Remove the volume pot from this point in the circuit and replace it with a 1M resistor to ground. There should be a series resistor from each input jack's hot lug feeding the ungrounded end of this 1M resistor.

We will now re-insert the volume control between the first and second tube stage. The volume control used to have a wire running from the input jacks to one outer lug; the other outer lug was grounded. You will now remove R6 (500k to ground); The non-grounded outer lug of the pot will connect to the end of C1 that used to connect to R6. The wire running from C1 to pin 1 of the 6SL7 should be lifted at C1 and connected to the center-lug of the volume control.

At this point, you have removed R6, moved the volume control to the place R6 used to be, and replace the original point for the volume control with a 1M resistor. Noise in the amp could be well lowered just by making this change.

Evaluate any remaining noise after making this change. You may/may not want to move the tone circuit to the traditional place right after the volume control, a la tweed Princeton. Remaining noise could be tube-related, or due to old noisy resistors, etc.

[Tiny_Daddy]

Take a look at the Hoffman schedule 40 schematic for example.

[SIG]

Thanks to both of you for the quick replies, awesome and supportive. I attached a similar schematic wich I'm considering using as a template for the front end that will enable me to have both volume and treble/tone control. The attached Supro Spectator schematic is what I'm considering. Thinking outloud here and appreciate feedback.

Parts removal:
1. Remove the current tone pot from pin 5 of the 6V6, it's wired there now, the schematic says pin 3 but the schematic is wrong there. Unwire the tone pot completely and get it ready for rewire.
2. Unwire the volume pot from pin 4 of the 6LS7 and unwire all the input jacks.
3. Unwire the 6SL7, almost completely except for the heater pin 7.

Reassembly:
1. Using the Supro Schematic, on the input jacks, wire the tips of the jacks via two 33k resistors into a 1MoHm resistor to ground, and a lead to pin 4 of the 6SL7. This is slightly different to the supro schematic, but following thetip you guys gave me.
2. The rest of the wiring, follow the Supro Spectator wiring for the 6SL7 and 6V6.
Thougts?
R, SIG

[HotBluePlates]

If completely removing the 6SL7 parts and rewiring helps you make the changes, go ahead. It is, however, adding extra chances for errors.

You could simply make the changes I mentioned. But I also understand the fun behind scrapping the old and building anew.

[SIG]

Thanks HotBluePlates!  I'll likely take the less evasive approach first and just try your suggestions. After hearing from you guys, I took a stab at merging and modifying my schematic for the Eastern Amp, merging it with the Supro Spectator.
Appreciate your quick look at the attachment now, especially on the input. I modified the spectator input that had 3 jacks to 2 jacks. Let me know what you think about the resistor values, 2 100oHm resistors to the 1MoHm good?

Thanks for your feedback! Yes, it's fun.

Paul

[SIG]

HotBluePlates, et al...
Today, I ordered the preamp resistors and caps for the front end of a Princeton 5B2 to rebuild this pup. I
I don't have the resistors on hand, but have a few caps. Ordered Allen Bradleys! Also ordered two new 1M Pots to replace these 60 year old pots in case they are a slight source of noise.
Without have the 1 Meg resistor to ground nor the resistors between the hot leads/tip of the input jacks to pin 4, I went ahead and made the changes HotBluePlates suggested and it was significantly less noisey, louder and better! I hope that once I get all the parts in, it will lower the noise floor even more and I'm sure it will.

Thank you so much for freely helping a novice like myself!

Hopfully this coming weekend Santa will deliver my parts, to include a new 6SL7. I'll post additional feedback for those who are interested and for the history of this rare amp.

Highest reguards, thanks again, Happy Holidays!!!!

Paul
www.myspace.com/paulsigmon

[HotBluePlates]

Glad it's working out so far Paul!

[SIG]

Hot Blues Plate, et al... again thanks for your help with wiring the 6SL7.  Still struggling with this little champ like amp, should be a lot simpler and I'm sure I've made it harder than it is..

The pre-amp section is clean and clear.. no squeal up to 10 on the volume!

Now, however, I still have noise that I need to rid from this amp. My schematic that I post a few weeks ago, on the Eastern Amp, is not accurately displaying my PT wiring to my rectifier and heaters. Specifically:
 
1. High Voltage Secondary Winding. Schematic shows center tap to ground, and brown HV wires to pin 3 & 5 on the 6X5. Actually wiring.. the Transformer, (only marking I can find is the numbers 841) HV winding wires are golden and red colored (not brown) but there are two of them and there's no CT wire that I can see. I looked too, pulled the PT, only 6 wires in total including primarys. One of the HF seconary wires is wired to ground, the other is wired to Pin 5 of the 6X5. Pin 5 is strapped to Pin 3 of the 6X5. Pin 8 of the 6X5 is wired to an 8mfd 450v cap and then to ground. HV wires measured approx 261.5VAC.
 
2. Heater wires: Like the high voltage wires, but these are blue green colored.. One lead is wired to the same ground connection as the HV lead that is wired to ground. The other heater lead is wired to pin 2 of the 6X5. Pin 7 of the 6X5 is gounded at the same location as the HV cap mentioned above. The 6V6 and 6SL7 tubes both have one of the heater pins wired to ground and the other heater pin is connected in series with the 6X5 pin 2. Heater wires measured approx 7.8VAC hot..
 
So, in short, I've read a bunch of stuff here online about "Virtual Center Taps when older small transformers don't have CTs..."  I attempted a rewire of the heater wires and although I though I did a nice looking job, twisted all the 20guage teflon coated silver stranded wiring that I bought. The noise didn't go away. The Virtual Center Tap I implemented, was I first ran the heater wires to the pilot lamp that wasn't wired at all previously.. From the pilot lamps positive and negitive leads, I ran 100oHm resistors tied together to ground. Prior to powering up, from each heater pin, I checked resistance to ground and oHmed out aproximatly 50oHms. I'm not touching anything at all on the heater leads and they look nice... the 7.8VAC measurement I mentioned above was taken with this virtual CT in place, without any tubes in the amp.
 
I'm not sure if the High Voltage windings need a virtual center tap or not.. I've been browsing through forums and sending emails to gentleman like yourself trying to better understand how to wire up this little champ/valco like amp but I haven't yet found a clear cut course of action. I just keep trying different things and I've all but completely hacked up the amp.
 
Attached is my latest find in my research. This amp appears to show a transfomer without true center taps (i believe), and it looks to have two 375oHm resistors put in before wiring the HV wires to pin 3 & 5 of the 6X5.
 
Appreciate anything you might be able to tell me, brain is scrambled. This should be simple.
 
Regards,

[sluckey]

One of the HF seconary wires is wired to ground, the other is wired to Pin 5 of the 6X5. Pin 5 is strapped to Pin 3 of the 6X5. Pin 8 of the 6X5 is wired to an 8mfd 450v cap and then to ground. HV wires measured approx 261.5VAC.

That's perfectly OK. It's wired as a standard 1/2 wave rectifier. The 1/2 wave rectifier was very common in small amps and radios. The resulting B+ needs more filtering than a full wave rectifier.

[PRR]

> I still have noise

Hissss? Hummm? Buzz? Radio stations? Chitterings?

[SIG]

Understand it should be OK and it's wired as half wave rectifier... thanks for your comment.

The issue I'm having, (I obviously wasn't clear, my fault) is that my amp, (Eastern Amp) doesn't show it's wired as half wave rectifier in the schematic. See original schematic posted hereto for the Eastern. It just has a High Voltage and a Heater tap wired to ground and no Center Taps. No filtering whatsoever.

This is why I posted and the (WARDS AIRLINE) schematic I just fould in my "The Tube Amp Book" that uses 6X5 & 6V6.. I was thinking I should try and wire up my amp like the Airline amp or get some advice here from others that might have experience with the 6X5 in a champ like amp. Like I said, I tried lifting the heaters and "floating" them in parallel wiring with a virtual CT, and from my ears, the noise increased by 3db or so. At this point, unless I can get some ideas on how to better wire this tranny to the 6X5, I'll just put it back to stock.

Any suggestions on filtering?

Any suggestions on if I should continue working out the virtual Center Tap for the heaters?

Any suggesions on filtering the High Voltage taps, currently, no filtering?

Thank you!

Paul 

[sluckey]

Your artificial center tap on the heaters should be fine.

my amp, (Eastern Amp) doesn't show it's wired as half wave rectifier in the schematic. See original schematic posted hereto for the Eastern.

Yes, I know. But your earlier description of the actual wiring says it is indeed a half wave rectifier. And without a center tap on the high voltage winding, all you can ever have with that 6X5 is a half wave rectifier. There is a simple trick to using a hybrid full wave rectifier with that PT, but it will take the B+ up to about 370V (which should be fine for those tubes). All you would need is two 1N4007 diodes and a little rewiring on the 6X5 socket.

It's not uncommon to see discrepancies between actual wiring and a hand drawn schematic. How do you know that C. J. Poulos got it right???

Any suggesions on filtering the High Voltage taps, currently, no filtering?

I don't understand this question. Your original schematic shows plenty of filtering on the B+. And your earlier statement "Pin 8 of the 6X5 is wired to an 8mfd 450v cap " means there is filtering in the actual amp.

[SIG]

So, I guess what you're saying is I could combine my 6X5 with diodes to rectify the other half of the way, correct? I guess this could lower the noise floor?

Regarding the filtering, yes, I was wrong. I didn't really consider the 8mfd cap as filtering initially, I normally thinking of filtering as and/or/nor gates and combinations of resistors/caps.. I'm an old Navy Radioman and that's how I was taught in school. But I see your point. Perhaps raising the value of the 8mfd cap to 16mfd or higher would bring that hum down?

Again, I do appreciate your feedback. I'm a novice, I've successfully restored 2 amps, this is my third.  It's additicting.

Paul

[PRR]

> I normally thinking of filtering as and/or/nor gates

Logic gates? "Thinking" doesn't fix power problems.

> and combinations of resistors/caps..

It's in there. Rectifier feeds C-R-C filter, through the OT/6V6 and back around. Analysis shows big raw AC in yellow, sorta-smooth DC on the first cap red, smoother DC on the second cap green.

[SIG]

Dang you guys know your ship... appreciate all the free knowledge sharing here and for helping me follow the signal flow, it's a lot clearer to me now and I'm going to fix the problem, it's in the filtering, I know it.

Back in a tic.

Paul