To add further to the mix, here is an archived thread from eHam forums on improving the 10 Meter input circuit:
/g/DRAKE-RADIO/files/Drake%20L7%2010%20Meter%20High%20Input%20SWR%20complete.pdfOne method I have heard of to isolate the HV feed while working on the amp live is to secure the end of the cable inside a glass jar.
73
-Jim
NU0C
On Mon, 15 Jan 2024 19:45:19 -0800
"Howard VE7IGA" <howard_kerster@...> wrote:
Yup I'm familiar with the two safety switches on my L7's.? And my L7's would both be imports.as they have stock 10m band positions.?On another note did I see that RV75' s are fetching $1000.00US dollars??!!! That's insane. I'll have to put my 2 in a safety deposit box.? ?hihi.Thanks again for everybody's help.? Howard VE7IGA?Sent from my Galaxy
-------- Original message --------From: "Evan via groups.io" <k9sqg@...> Date: 2024-01-15 7:19 p.m. (GMT-08:00) To: [email protected] Subject: Re: [DRAKE-RADIO] L7 input coil ajustment
Fellow Drake Enthusiasts,Two comments.First, unlike the L4B, the L7 has two (2) safety related devices. ?The first is the above chassis high voltage shorting mechanism, the other is a microswitch along the edge, on the underside.Second, there are at least three (3) different designs for enabling the bandswitch to go to the 10M position. ?The first is that little bar that can be removed from the underside of the RF deck; this was a joy for CBers. ?The other two methods are more involved, one of which has a miniature bolt and a round knurled nut; take precautions to prevent parts from falling into the RF deck topside.As a side note, tuning on 10 and 15 meters is extremely broad. ?And on some bands, the length of the coax between the amp and the driving rig can alter the tuning coil adjustments.Just my experiences, I'm not an expert.73,Evan, K9SQG
On Monday, January 15, 2024 at 03:53:58 PM EST, VE7PS <ve7ps@...> wrote:
Howard:I'll add two comments to David's instructions for adjusting the input tuning on the L-71)? Check out the L-4B instructions.? They got that correct and it's the same procedure.2)? While I would not personally recommend adjusting the input tuning with high voltage applied...for safety reasons...but?IF you choose to do so, keep in mind you would also have to defeat the HV interlock to do this with the lid off....which IS necessary to reach the coils.I recently did some work on an L-4B for a ham in Surrey, BC.? I did the input tuning on his amp after undoing some "magic nichrorme" mods and adding in some more modern ones (Electronic Specialties).? Note the input tuning is very broad, though perhaps due to aging of the caps, I did notice a slight improvement on some bands.? As such, I am not in any hurry to adjust the input tuning on my own amps, unless perhaps the tubes get changed at some point.Be careful!73PeterVE7PSOn Sat, Jan 13, 2024 at 11:07?AM Howard VE7IGA <howard_kerster@...> wrote:Hey guys, I'm going to be doing a input coil adjustment on my L7 amp. Eimac tubes are getting very soft and I'm replacing them with RF Parts matched pair.I've done this before and i'm very aware of safety procedures. It's been awhile.I just want to clarify a few things before I start. Procedure (F) I take it that the plate control should also be in the centre of the band I am adjusting , this is not mentioned in procedure. Also when increasing exciter output to achieve a .400 amp. reading on the grid meter, procedure (I) is this correct because my other L7 manual said plate meter.Lastly when tuning the plate control for dip in plate current, procedure (J) is it a greatest dip possible or just a slight dip in plate current??Thanks for any input you can provide. Howard VE7IGA
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73
-Jim
NU0C
Jim Shorney