Gibson EH 150

aabbs20 · Post by **aabbs20** » Wed Mar 25, 2015 3:04 pm

Hi all!

I'm a newcomer to the forum and a hobbyist builder. I've built a number of tweed circuits and I'm thinking of a Gibson EH 150 next. It has been tough to find info and other builds. Any one have experience with this circuit?

Thanks!

Stevem · Post by **Stevem** » Wed Mar 25, 2015 3:19 pm

I assume you are thinking of building one of the latter one that do not use a transformer for a phase splitter as they are gonna be hard to come by!

M Fowler · Post by **M Fowler** » Wed Mar 25, 2015 3:59 pm

Search function:

https://tubeamparchive.com/viewtopic.ph ... bson+eh150

https://tubeamparchive.com/download/file.php?id=24587

https://tubeamparchive.com/viewtopic.ph ... bson+eh150

https://tubeamparchive.com/download/file.php?id=16384

https://tubeamparchive.com/viewtopic.ph ... bson+eh150

https://tubeamparchive.com/viewtopic.ph ... bson+eh150

https://tubeamparchive.com/viewtopic.ph ... bson+eh150

aabbs20 · Post by **aabbs20** » Wed Mar 25, 2015 4:12 pm

Thanks! I did a bit of fruitless searching but I must have done something wrong because those results didn't turn up.

M Fowler · Post by **M Fowler** » Wed Mar 25, 2015 4:17 pm

No problem.

Teleguy61 · Post by **Teleguy61** » Wed Mar 25, 2015 4:39 pm

Search function takes a bit of learning.
Note that Mark used EH+150 in his search.
Use of the + sign is important.

aabbs20 · Post by **aabbs20** » Mon Mar 30, 2015 2:38 pm

What transformers did you guys use in your builds? David you used an all TP25, but are there better options? Do you guys have a recommendation for a low voltage secondary PT? Is it better to get a higher secondary and drop it with a Zener?

Thanks.

Post by **Colossal** » Mon Mar 30, 2015 3:13 pm

aabbs20 wrote:What transformers did you guys use in your builds? David you used an all TP25, but are there better options? Do you guys have a recommendation for a low voltage secondary PT? Is it better to get a higher secondary and drop it with a Zener?

Thanks.

The target plate voltage is 275-290VDC, Class A cathode bias, push-pull. About 20VDC on the cathodes. The original amps (Types II, III, and IV) used a Thordarson T-40069 PT which was 408-0-408. Yes, that's right. There was a field coil speaker inline with the B+ string which provided a voltage drop (use a choke to sub for the field coil) but also, and importantly, there was a 20k 25W resistor TO GROUND in the B+ string, parallel to the reservoir cap.

aabbs20 · Post by **aabbs20** » Mon Mar 30, 2015 5:09 pm

So I should look for a PT with something around 400 on the secondary?

M Fowler · Post by **M Fowler** » Mon Mar 30, 2015 6:29 pm

I used:

Hammond 274BX 750vct 175mA

Hammond 1645 30w 128mA 5k primary to 4/8/16 secondary

Hammond 158M choke 10H 100mA

Post by **Colossal** » Mon Mar 30, 2015 6:34 pm

aabbs20 wrote:So I should look for a PT with something around 400 on the secondary?

It depends if you are trying to make a historically accurate clone and/or whether you want solid state or tube rectification. The originals were tube rectified (5U4G). If you will not be using a field coil, then I would use a 1k 25W resistor in the first Pi filter.

aabbs20 · Post by **aabbs20** » Mon Mar 30, 2015 7:41 pm

M Fowler:

Thanks a ton! What did your B+ end up at? Your build looks great too, I'll be referencing it a bunch. Did you punch your own chassis?

Colossal:

I definitely want to use a tube rectifier and be somewhat historically accurate. I won't be using a field coil speaker but would love to have the plate voltage nice and low. Thanks for the tip on the 1K 25W resistor as well.

M Fowler · Post by **M Fowler** » Mon Mar 30, 2015 9:32 pm

aabbs20

You should see Colossal's build it's really impressive.

Yes I punched my own chassis a Watt's 17.5x8x2.5 I believe and is in my opinion too large. Long wire runs everywhere.

119AC wall
B1 473
B2 447
B3 390
B4 203
Plates 447 6L6
Screens 439

David Root · Post by **David Root** » Mon Mar 30, 2015 9:45 pm

Dave, I originally built mine to the 400V version in Tino Zottola's book. I used the Allen TP25 because it was about the right voltage and it fit the cut out/mtg centers in the Mojo knockoff BF Princeton Reverb chassis I used. Ended up with ~375V plate using a Hammond 158Q choke (5H, 150mA), CL feed.

When I decided to go to the lower voltage, as originals ran about 270V just like the 6L6 data sheets of the day, I just changed the CL feed to LC choke feed by reversing the positions of the choke and the reservoir cap, and also changed the rectifier from a 5R4 to a 5AR4, to get back up to 280V plate. An old Mullard, not a Sovtek, which won't get down to 280V in that scenario.

BTW it took me a while to figure out what the original plate voltage was, I finally found it, I think it was on an EH185 schematic IIRC, which by that time (1941-2) was the same as the EH150.

Also, I heard that the 6N7 PI could be noisy/hummy and wondered if anyone had tried a 6SN7 instead, and if so did that kill the residual hum? I used the 6N7 and even choke fed it's not quite as quiet as I would like, although I wouldn't be surprised if it's quieter than an original EH150.

Post by **Colossal** » Mon Mar 30, 2015 10:14 pm

aabbs20 wrote:Colossal:

I definitely want to use a tube rectifier and be somewhat historically accurate. I won't be using a field coil speaker but would love to have the plate voltage nice and low. Thanks for the tip on the 1K 25W resistor as well.

I'll have to look at my notes on the field cool resistance but IIRC, 850R - 1k should be about right. If you use a 390-400VAC secondary and a 5U4G, be sure to use that 20k 25W bleeder resistor to ground, parallel to the first Pi filter.

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