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Old 22nd October 2008, 02:47 AM   #1
Trout is offline Trout  United States
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Default Do New JJ GZ34's have less B+ Drop?

Do Current Production GZ34's have less voltage drop than NOS?

Case:

So I grabbed this 1964 Fender Blackface Deluxe at a thrift store a couple weeks ago for $35.00. It was dirty, torn grill and tolex, torn speaker, and no tubes. I figure for $35.00 I cant go wrong.

I pull it apart and of course the PS caps are leaking, no problem. The OT has a wired pulled out Oh Well DOA Still a cheap project. I test the PT, its deader than dead.

So, I order up a set of Hammond guitar series transformers since they sell " Proper" replacements. The Hammond part numbers are (PT 290BX) ,and (OT 1750H)

While waiting for them to arrive, I replaced all of the electrolytic caps, (PS, bypass & Bias) Checked out all of the resistors for excessive drift, replaced a couple, no big deal.

The transformer arrive fairly fast and I proceed to mount everything up.
Now, I install a complement of JJ tubes, GZ34, 6V6S, 12AX7's, power it up, proceed to check the bias. The anode reads 462V??, screen 465V?? The bias pot range allows me to go from 15ma - 30ma per tube. The kicker is the original schematic says 410V anode, and 405V screen.

Do new production GZ34 rectifiers have less voltage drop than NOS? The PT is supposed to be a 120V 60hz primary so its not likely I would get that much B+ over spec voltage with all other ratings being equal.

PT:290BX
Primary: 120 volt, 60 Hz
Secondary:340 VDC @ 120 mA FWCT, 330-0-330 VAC @ 120 mA, with 50V bias tap
Filament winding 1: 6.3 V, 3 A
Rectifier Filament: 5 V, 3 A

OT:1750H
Audio Watts (RMS): 20
Primary Impedance (Ohms): 6,600 CT
Secondary Impedance (Ohms): 8
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Old 22nd October 2008, 03:55 AM   #2
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Dude,

With few exceptions, Hammond's 2nn series power trafos are "speced" at 115 VAC on the primary. Look here. In addition, Hammond has a reputation for being over voltage. I saw that the guitar stuff is rated for 120 VAC, but ...

Try a 5U4GB as the rectifier to bring the rail voltage down. AFAIK, JJ's 5AR4 conforms to published specifications.
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Old 22nd October 2008, 04:00 AM   #3
Trout is offline Trout  United States
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Think a 5Y3GT would hold up in there? After all, were talkng about a 50V over range.

The JJ tubes can handle the voltages, but it kind of limits the choices on which 6V6's can be used.
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Old 22nd October 2008, 04:29 AM   #4
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Quote:
Originally posted by Trout
Think a 5Y3GT would hold up in there? After all, were talkng about a 50V over range.

The JJ tubes can handle the voltages, but it kind of limits the choices on which 6V6's can be used.

Yeah, a 5Y3 should survive, given the 120 mA. of B+ rating for the trafo. If B+ comes in too low, with a 5Y3, try a 5R4. Watch the 1st filter cap. size, when 5R4s are used.

If the budget can stand the bite, try the Saratov, Russia, made TungSol "reissue" 6V6.
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Old 22nd October 2008, 04:34 AM   #5
Trout is offline Trout  United States
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Quote:
Originally posted by Eli Duttman



Yeah, a 5Y3 should survive, given the 120 mA. of B+ rating for the trafo. If B+ comes in too low, with a 5Y3, try a 5R4. Watch the 1st filter cap. size, when 5R4s are used.

If the budget can stand the bite, try the Saratov, Russia, made TungSol "reissue" 6V6.

Yeah, I was worried about the B+ on the caps, I used FT 20uf/500V and when I saw 460+ volts I freaked!

What the heck were they thinking with these transformers? That is a pretty significant jump.

Thanks for the quick responses!!
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Old 22nd October 2008, 04:45 PM   #6
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It seems like I had an old Deluxe Reverb that I was repairing one time or another and it was in the 450 volt range on the B+. Once the amp warmed up for a while it dropped off somewhat and it wasn't a problem. I wonder if the Hammond transformer isn't spot on correct for a Deluxe because back in the 1960's wasn't it 110 volts ac instead of the 115-120 volts we generally have today?
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Old 22nd October 2008, 06:33 PM   #7
Trout is offline Trout  United States
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Quote:
Originally posted by DaveMcLain
It seems like I had an old Deluxe Reverb that I was repairing one time or another and it was in the 450 volt range on the B+. Once the amp warmed up for a while it dropped off somewhat and it wasn't a problem. I wonder if the Hammond transformer isn't spot on correct for a Deluxe because back in the 1960's wasn't it 110 volts ac instead of the 115-120 volts we generally have today?

The Hammond data sheet says it is a 120v 60hz primary, but as Eli mentioned above, What Hammonds sheet say is not always correct.

I wrote Hammond about the issue, but as of yet have gotten no response.
I ran the amp about 2 hours, it sounds great, and biased at 20ma it does not seem to be getting excessively hot. The transformers remain cool to the touch after a constant 2 hour run.

I guess it will be OK, but I would have liked it to be closr to the
Schematics listed voltages.

Time will tell on how long the tubes last.
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Old 23rd October 2008, 12:21 PM   #8
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Quote:
Originally posted by Eli Duttman



Yeah, a 5Y3 should survive, given the 120 mA. of B+ rating for the trafo. If B+ comes in too low, with a 5Y3, try a 5R4. Watch the 1st filter cap. size, when 5R4s are used.

If the budget can stand the bite, try the Saratov, Russia, made TungSol "reissue" 6V6.
The TX may be rated for 120 mA, but the circuit is consuming more like 60. 5Y3 will do fine, and get type 6087 to keep the indirectly heated cathode like the original GZ34. All the 6087 I have seen are GE 5 star and have been quite tough looking( they're 6BL7GTB-sized ).
cheers,
Douglas
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Old 23rd October 2008, 05:34 PM   #9
Trout is offline Trout  United States
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Got a reply from Hammond,

Quote:
We are currently looking into your complaint. This is the first time we have received this type of feedback. Just a few questions to help us with the investigation:

1) Where are you located???

2) What is your line voltage??

3) Has this amp been “solid-stated” in the power supply?? In other words is the 5Y3GT still there AND connected??

THANKS
Regards
Ray Shatzel
HAMMOND MFG CO
Interesting question to me was " is the 5Y3 still in there and connected? "

The Blackface, & Brownface Deluxe series amps did not use a 5Y3.
Fact, the Tweed era Deluxe amps used 5Y3 and this transformer would be even more grossly off spec in a 5E3 Tweed Deluxe.

If someone was to put one of these transformers in a vintage unit and they did not upgrade the PS caps 16uf/450V I suspect the results would not be good at 465V.

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