Still messin' with my 52fh

[slohand42]

Actual Schematic

Here's the actual schematic of the "as built" grid leak preamp, now.



Ted

[Bruce / Mission Amps]

Here's the actual schematic of the "as built" grid leak preamp, now.



Ted

Other then loading the mic element down a little bit, what do you think the significance of the 100K resisitor is? With one input jack, I'd not use it but I haven't tried this setup.

[slohand42]

Other then loading the mic element down a little bit, what do you think the significance of the 100K resisitor is? With one input jack, I'd not use it but I haven't tried this setup.

Honestly, Bruce, I'm not sure what it does. I'm still a bit novice with some of this amp stuff, though I've been messing with it for a few years. I've seen grid leak set ups on the Gibson GA-20 and 20T that didn't have the 100K resistor to ground before the cap, but most examples do have it, so I left it in mine.

I guess I could try it without it easy enough and see if there is any difference good or bad.

It does sound pretty sweet as it stands, right now, though.

Ted

[slohand42]

OK, I take it back

Bruce, in looking more deeply into it, I decided to check out the old PA amps with "grid leak" that were supposedly the holy grails of harp tone in the old days.

Most of them did not have the 100K resistors in them. They didn't even have the 33K resistors. Their mic inputs went directly to the cap.

I guess I'll try that and see what comes of it.

Thanks for the question and input.

Still Messin', I guess.

Ted

[Bruce / Mission Amps]

...

Thanks for the question and input.

Still Messin', I guess.

Ted

Yeah, me too.... I'm never completely happy with a harp amp... and the players are all over the board with technique which ruins much of the tone tweaking.
I'm working on 2x10 or 1x12, twenty five to thirty watt harp amp project now and need to get further down the road on it.

[slohand42]

So, I did some more messin'. I first did a sound test as it was to get a base point to work with in my head. Then I removed the 100K resistor. You were right, Bruce. The 100K resistor was loading down the element. Removing it gave more "life" to the rig. I then removed the 33K in-line resistor to emulate the PA amps I had researched. This did effect tone a little, but not in a way that I was happy with. I put the 33K back in and am even more pleased than I was last week.

Just a note. With this set up, a player can get different voicing by compromising the cup around the mic. A full, air tight cup gives a "browner" tone if you will, while varying amounts of opening the seal on the cup brings out more grind and honkiness.

All in all. I like it.

Now back to the speaker trials. At present, I'm still running a Magnavox gold something or other 12". In the previous set up, it was the best out of many.

Again, thanks for the response and input.

Ted

[the wizard]

Yeah, me too.... I'm never completely happy with a harp amp... and the players are all over the board with technique which ruins much of the tone tweaking.
I'm working on 2x10 or 1x12, twenty five to thirty watt harp amp project now and need to get further down the road on it.

Bruce, Any updates in your new harp amp?

[Bruce / Mission Amps]

5E3 vs GA-6 vs 5E5A or 5F11 etc etc

Bruce, Any updates in your new harp amp?

I've been toying (actually already experimenting) with the using a 5E5A layout and a 1x12 cabinet... but in a single channel version and with some harp friendly mods and XLR line out.
My ultimate plan is to use a 30 watt, 12" smooth cone, Alnico speaker (a custom made speaker Adam from Tungsten Amps and I are working on) ... in conjunction with a "tuned", 8" Alnico or ceramic.. but I recently had an old Gibson GA-6 in for a nasty little hum problem and after getting that sorted out, I really liked the way it sounded... way better then a stock 5E3 Deluxe.

If you're interested, the harp player in a band I play Chicago blues drums in
( http://www.roadhousejoe.com/fr_index.cfm )

runs this blog and below here is a link to his comments about the 5E3 vs a GA-6:

Blues Harp Amps: Vintage vs. Vintage

The GA-6 is super simple so I thought I try something like that too.
I'm going to try MWJB's grid leak/contact bias scheme but with a pentode front end... where I could also apply a little compression circuit using a tiny DC feedback voltage to it's G2 (screen grid).
I don't know what to expect with this but that's the real fun in doing these things for me these days... ha ha...

[arnenym]

Rick write the Ga-6 lancer have grid leak bias, but at this schematic it have cathode bias input:
http://www.schematicheaven.com/gibso...ga6_lancer.pdf
And he put the 5E3 down because cone cry and ghost notes,. Aint that speaker issues?

[Bruce / Mission Amps]

Rick write the Ga-6 lancer have grid leak bias, but at this schematic it have cathode bias input:
http://www.schematicheaven.com/gibso...ga6_lancer.pdf
And he put the 5E3 down because cone cry and ghost notes,. Aint that speaker issues?

Well, he put down the 5E3 for harp use, it sounded great with a Strat.
Yes, cone cry and ghost noting could be speaker issues. What we were hearing was the ghost noting with hard reed bending.
The speaker in the 5E3 was also a real late 50's Jensen but I think it was recently reconed by someone.... possibly Weber.

As for the GA-6 schematic, no this one was not cathode biased.
The GA-6 amp I had was "grid leak" bias or sometimes called "contact bias".
Although not quite visible in the picture, with a big hefty 5meg resistor on each grid with a .005uF cap in front of it.

Below is a picture of the open chassis from Ricks harp blog website.
Note in the pictures the old yellow Astron caps coming from the input jacks on the right side of the chassis as viewed.


http://www.bluesharpamps.blogspot.com/

[arnenym]

Yes it propably have been modded or its a very early model. But more important is, when i look at the pics again i see the gibson have newer electrolyths. Bad old filtering could give ghostnotes with harp.

[Bruce / Mission Amps]

Yes it propably have been modded or its a very early model. But more important is, when i look at the pics again i see the gibson have newer electrolyths. Bad old filtering could give ghostnotes with harp.

Yes, since the owner of the 5E3 is going to be selling the amp, he wanted to keep the amp as original as possible and didn't want to change anything on the board or replace the input jack and bad volume control pot, which were the main causes of his noise problem.