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Author Topic: 40M QRP amp from 807s?  (Read 1148 times)

KM1H

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Re: 40M QRP amp from 807s?
« Reply #15 on: September 30, 2021, 09:14:28 AM »

Quote
Some brands of 807 had the reputation of being prone to VHF parasitic oscillations: not a problem i've ever had, but I've always used something like 47 or 68 ohm non-inductive resistors with very short leads right up at the grid and screen grid pins at tube socket as well as the usual parallel resistor/inductor arrangement at the plate cap. Running as a linear may require neutralising on the higher bands; again, parallel operation is easier if you need to add neutralisation at a later stage.

My builds are either grid driven using a resistor to partially swamp it but still requiring a LC circuit; fine for QRP drive. Using 5 modified 1625's in GG for SSB, one to drive the 4 it was stable up to 15 with no resistor but TVI was horrendous on 15 on old B&W sets with a 21 mc IF. Drive was from a CE 10B which had no TVI proofing either.

The other was directly copied from the National NCL-2000 and was all resistive with connections for either low (10-20W) or high drive up to 100W. Ive been using 15W drive on a 6M conversion for 1200W since the 60's
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #16 on: October 01, 2021, 07:04:48 PM »

Any of you guys have any of the old school plug in coils in your junk boxes? Looking for some dimensions/coil counts of the Bud or B&W Juniors as well as the Bud RCL or B&W BL coils. I could probably crunch the numbers out based on the capacitance but it'd be nice to have a confirmation thereof. Specifically the 40M but I'd take an 80/20/10 as well.
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WA3EEC

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Re: 40M QRP amp from 807s?
« Reply #17 on: October 03, 2021, 09:47:45 AM »

I have a few National Center Link Coils 80C, 40C (have 3), and 20C and the socket for them.

If someone would like them I can send you a picture and you can have them for the cost of shipping.

Lad WA3EEC
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #18 on: October 03, 2021, 01:58:49 PM »

Wow, I'd be blown away for that. PM inbound.
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K3UIM

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Re: 40M QRP amp from 807s?
« Reply #19 on: October 03, 2021, 02:12:11 PM »

As I've said before, "You gotta love this group!" An answer for every question, a solution for every problem and a part, or parts, for every project's need.
Charlie
On Edit: But no hangman's noose for a troll! Pity.  ::) 8) ;D
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Charlie. K3UIM
Where you are: I was!
Where I am: You will be!
So be nice to us old fogies!!

WA3EEC

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Re: 40M QRP amp from 807s?
« Reply #20 on: October 04, 2021, 10:24:32 AM »

Wow, I'd be blown away for that. PM inbound.

Send me your contact info.
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #21 on: October 04, 2021, 10:50:29 AM »

Wow, I'd be blown away for that. PM inbound.

Send me your contact info.

Thought I sent you one, probably what I get for thinking. :D Sent, get back to me if it doesn't get your direction.
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WA3EEC

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Re: 40M QRP amp from 807s?
« Reply #22 on: October 05, 2021, 05:14:33 PM »

Did not get a PM yet.
Email is mycall-at-ARRL.net
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #23 on: October 05, 2021, 07:32:44 PM »

Did not get a PM yet.
Email is mycall-at-ARRL.net

email sent from my gmail.
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #24 on: October 10, 2021, 08:07:20 AM »

I got the coils! I will try to get some pics up in a bit. They look used but lovingly so.

 There are pairs of each in 20, 40 and 80m. I am going to probably use one set on input and one on output.

Right now the base plan is to use a chassis from a Masco PA audio amp. Really wish I had left this one in tact but took it apart a long time back. Youthful inexperience at hoarding I guess.

It was a gift from a ham mentor that ran a tv repair store some years back. Haven't heard about him in forever, hope he is not sk at this point.

The PSU may be a second chassis. Just not sure.

I have it partailly designed but I am still trying to figure the bias supply out. I have a transformer I want to use however I am just not sure about the voltage since my gear is in storage.

I have also not figured out a bias regulation circuit yet since I want to be able to have the option of swinging bias from about -40 to -70 volts.

I may initially cheat the screen supply and use my bench psu which is based off the vr circuit in a hp vtvm. I intend on a similar circuit for this as well. If I run class c for cw it may be I initially simplify the circuit for the build as well and just use vr tubes vs a series regulator.

Plate power will be a standard lc linear psu. Nothing special.

TR switching will likely be via a MASTR Progress relay. any issues with that potentially? They were vhf and uhf units so I think it would be okay. Then again I should check and see if they were power only or dc only.
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #25 on: October 10, 2021, 08:23:15 PM »

Just wanted to throw this in here real fast so that some one searching for these questions doesn't have to figure it out themselves or buy coils to do it. These appear to be National Branded coils (by the NC on them) so although YMMV it wouldn't surprise me if they were relatively similar (if not identical) to other homebrew based coils such as B&W, Bud etc.

These are center fed coils and I'm going to give overall dimensions and wire gauge as well as turns. They are air core inductors with strips of plastic to hold them together and have a center tap in the primary that divides them evenly. Should be useful to someone wanting to replicate them. The uH given is based on a simulator NOT based on actual measurements. If I have a way to get those later on I'll add them. It's plausible these would be a good start for end fed coils as well but I can't attest to that for fact.

All units inches.

Secondary (all coils)
OD      length turns AWG uH (calculated)
1.475  .227    3       ~19    .5496
Part:  OD (primary)  length (primary)   Turns (primary) AWG    uH (calculated)
80C   1.24                1.65                     56                     24         54.596
40C   1.28                1.443                   28                     20         15.9052
20      1.305              1.137                   14                     18        4.8397
10      1.267              1.308                   8                       ~19      1.3675
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #26 on: December 21, 2021, 10:44:58 PM »

Finally a brief updateish post. I am starting to get back to this, I got my worldly possessions to the new house Sunday and have been unpacking. I thought for a bit I had lost the tubes! I would have subbed something in but still.



My PA amp chassis. I do have real estate concerns and am thinking something else.



I had no sockets so I got some import ones. The cap is 2*100pf and those are a few of the coils that were donated. What is the 5 pin plug called?  I am thinking trf input and output although I may try a toroid. I still need plate caps although alligator clips will suffice for now or home bent metal strips.



I think I added to this box over time. Obviously a hamfest item. Definitely didn't pay 10 bucks.



This guy is an oddball. I do not believe it an 807 and wouldn't run it as one.



Got 5 to play with, the mystery tube and a 6ew6 stow away.

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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #27 on: December 29, 2021, 07:31:56 AM »

So I started playing around with a prospective fixed bias transformer yesterday. It puts out about 45.2 open and with a load of 3k I get 43.4v. Any opinions on if this would be stiff enough to bias a pair of 807s?
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #28 on: December 29, 2021, 12:50:36 PM »

Testing 807s. I either have a saggy  hv psu or a resistance in the circuit. The latter is what I suspect. The PC PSU to the right of the soldering iron is my variable high voltage PSU based on an HP VTVM circuit loosely. It also supplies filament voltage. The PSU on the left is supplying variable bias. The green meter measures it's voltage. The left Simpson 260 measures plate voltage and the right plate current. The goal is to find a couple tubes that chart over a few bias voltages with similar current. I am troubleshooting the voltage drop issue still so this is in the early phases.

« Last Edit: December 29, 2021, 12:52:55 PM by AC9QC »
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AC9QC

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Re: 40M QRP amp from 807s?
« Reply #29 on: December 29, 2021, 10:34:26 PM »

Tested these tubes using 250v on the screen and plate. The right column is bias voltage.

I think most of these were fairly well used up based on the results of #1 unless I need higher testing voltage. Either that or #1 is a ringer.

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